Electronic watch

ABSTRACT

An electronic watch with a two-coil stepper motor including: a magnetized rotor; a stator including: first and second stator magnetic-pole portions, which are formed so as to oppose to each other through the rotor; and a third stator magnetic-pole portion, which is formed between the first stator magnetic-pole portion and the second stator magnetic-pole portion so as to face the rotor; a coil A to be magnetically coupled to the first stator magnetic-pole portion and the third stator magnetic-pole portion; and a coil B to be magnetically coupled to the second stator magnetic-pole portion and the third stator magnetic-pole portion; and a high-speed drive pulse generation circuit configured to output a drive pulse for driving the rotor to the coil A or the coil B, and wherein the rotor is rotationally driven in increments of 360° due to a drive pulse train formed of the plurality of drive pulses.

TECHNICAL FIELD

The present invention relates to an analog indication-type electronicwatch using a two-coil stepper motor.

BACKGROUND ART

Hitherto, in general, an electronic watch including analog indicationmeans has hands that are driven by a stepper motor. This stepper motorincludes a stator to be magnetized by a coil, and a rotor that is adisc-shaped rotary member magnetized into two poles. For example, thestepper motor is rotationally driven by 180° for each second to indicatethe time with the hands.

In such an analog indication-type electronic watch based on a steppermotor, a position indicated by a second hand or the like deviates dueto, for example, a backlash of a wheel train configured to move thehands, which causes the second hand or the like to deviate from a dialdivision. In addition, in order to prioritize miniaturization of thestepper motor, the holding torque of an indicator wheel is reduced,which leads to a problem that, for example, the position of a hand getsout of order due to an impact or the like.

In order to solve such a problem, there is proposed an electronic watch,which is configured so that a drive pulse for driving the stepper motorhas a two-step configuration including a first drive pulse and a seconddrive pulse, and includes a motor control circuit configured to set anoutput interval between the first drive pulse and the second drive pulseto 50 mS or less (see, for example, Patent Literature 1).

According to the electronic watch of Patent Literature 1, as describedtherein, it is possible to set the rotation speed of a rotor higher thanusual, for example, twice the rotation speed, by outputting the firstdrive pulse and the second drive pulse having an output interval of 50mS or less, and hence a speed reduction ratio from the rotor to a secondindicator wheel can be increased, to thereby be able to increase theholding torque of the hands and be able to alleviate the deviation ofthe positions indicated by the hands due to a backlash.

In addition, as a drive method for a stepper motor used in an analogindication-type electronic watch, there is proposed a method involvingconnecting a first coil and a second coil to a common connection pointand switching a current to be applied for each of three phases (see, forexample, Patent Literature 2).

CITATION LIST Patent Literature

[PTL 1] JP 3166654 B2 (page 2, FIG. 1)

[PTL 2] JP 2016-178742 A

SUMMARY OF INVENTION Technical Problem

However, in the electronic watch presented in Patent Literature 1, therotor is rotated by one revolution (360°) through two-step drive, andhence there is a time interval between the first drive pulse and thesecond drive pulse, which causes, for example, deceleration, vibration,stop, and reacceleration in the movement of the rotor. As a result, thehands move in an awkward and unnatural manner to exhibit poor-lookingmovement, which causes a problem of causing a user of the electronicwatch to feel discomfort.

In addition, when the time interval between the first drive pulse andthe second drive pulse is reduced in order to avoid this problem, thesubsequent drive is performed while vibration after the rotation of therotor has not converged yet, and hence the frequency of an abnormaloperation that reverses the rotor increases, which leads to a fear thata malfunction may be caused to a stepper motor. Further, the rotor isrotated by one revolution (360°) through two-step drive in the samemanner as the related-art drive, and hence a limitation is imposed onthe rotation of the rotor at high speed, which is not suitable for thehigh-speed drive of the stepper motor.

The present invention has an object to solve the above-mentionedproblems and provide an electronic watch capable of driving the movementof the hands smoothly at high speed by rotationally driving a two-coilstepper motor in increments of 360° per step.

Solution to Problem

In order to solve the above-mentioned problems, an electronic watchaccording to embodiments of the present invention employs configurationsdescribed below.

According to one embodiment of the present invention, there is providedan electronic watch including: a two-coil stepper motor including: arotor magnetized into two poles or more in a radial direction of therotor; a stator including: a first stator magnetic-pole portion and asecond stator magnetic-pole portion, which are formed so as to oppose toeach other through the rotor; and a third stator magnetic-pole portion,which is formed between the first stator magnetic-pole portion and thesecond stator magnetic-pole portion so as to face the rotor; a firstcoil to be magnetically coupled to the first stator magnetic-poleportion and the third stator magnetic-pole portion; and a second coil tobe magnetically coupled to the second stator magnetic-pole portion andthe third stator magnetic-pole portion; and a drive pulse generationcircuit configured to output a drive pulse for driving the rotor to thefirst coil or the second coil, wherein the drive pulse includes aplurality of drive pulses, and wherein the rotor is to be rotationallydriven in increments of 360° due to a drive pulse train formed of theplurality of drive pulses.

With the electronic watch according to one embodiment of the presentinvention, the rotational drive in increments of 360° per step isenabled by a drive pulse train formed of a plurality of drive pulses, tothereby be able to achieve the high-speed drive of the stepper motor. Inaddition, the rotor is rotated by one revolution (360°) for a shortperiod of time without stopping, and hence the movement of the handsbecomes smoother, to thereby be able to provide an electronic watchhaving satisfactory appearance without awkwardness. Further, the steppermotor is driven in increments of 360° per step, and hence a gear speedreduction ratio can be doubled (to 1/60) compared with a gear speedreduction ratio of 1/30 of a wheel train in the related-art rotation by180° per step for the stepper motor, and the torque of the hands can beincreased, which improves the impact resistance of the hands.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the drive pulse train is formed of threedrive pulses of the plurality of drive pulses.

With this, the rotational drive by 360° per step can be achieved by asfew as three drive pulses, and hence it is possible to perform thehigh-speed drive compared with the related-art two-step drive, whichenables the hands to be moved in the fast-forwarding operation of thehands at a speed higher than in the related art.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the electronic watch is configured toswitch between high-speed drive, in which the rotor is to berotationally driven in increments of 360°, and normal drive, in whichthe rotor is to be rotationally driven in increments of 180°, and thatthe rotor is to be driven in the high-speed drive at a frequency higherthan in the normal drive.

With this, it is possible to switch between the high-speed drive, inwhich the rotor is to be rotated in increments of 360°, and the normaldrive, in which the rotor is to be rotated in increments of 180°.Therefore, for example, it is possible to perform the high-speed drivebased on the rotation by 360° per step when the hands are subjected tothe fast-forwarding of the hands, while it is possible to perform thenormal drive in increments of 180° per step in the case of moving thehand every second or other such case of normal hand movement.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the electronic watch further includes: afirst two-coil stepper motor to be subjected to the high-speed drive;and a second two-coil stepper motor to be subjected to the normal drive,and that a drive frequency of the second two-coil stepper motor is lowerthan a drive frequency of the first two-coil stepper motor.

With this, the first two-coil stepper motor to be subjected to thehigh-speed drive can be used for driving minute-hour hands, which arerelatively large in hand shape and low in drive frequency. Theminute-hour hands are relatively large in shape, which causes the impactresistance to be important, but are low in drive frequency, whicheliminates the importance of the low-power-consumption drive. Therefore,the first two-coil stepper motor subjected to the high-speed drive,which is configured to rotate the rotor in increments of 360°, tothereby double the gear speed reduction ratio to increase the torque ofthe hands and improve the impact resistance, is suitable for theminute-hour hand drive. Further, the second stepper motor to besubjected to the normal drive can be used for driving a second hand,which is relatively small in hand shape and high in drive frequency. Thesecond hand is relatively small in shape, which eliminates theimportance of the impact resistance, and is high in drive frequency,which causes the low-power-consumption drive to be important. Therefore,the second two-coil stepper motor subjected to the normal drive issuitable for the second hand drive.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the electronic watch is configured toselect a high-speed drive pulse train or a normal drive pulse byswitching a timing to select a specific drive pulse from the drive pulsetrain.

With this, it is possible to select and output the high-speed drivepulse train or the normal drive pulse by arranging one drive pulsegeneration circuit to switch a timing to select a specific drive pulsefrom the output drive pulse train, and hence it suffices that only onedrive pulse generation circuit is provided, which is advantageous inthat the circuit scale of the electronic watch can be reduced.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that one terminal of the first coil and oneterminal of the second coil are short-circuited.

With this, it suffices that the number of drive waveforms to be suppliedis three and that the number of transistors is small, and hence effectsof miniaturization of the circuit scale and reduction in cost areexpected to produced.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that at least one of the plurality of drivepulses included in the drive pulse train is formed of a pulse forexciting the first coil and a pulse for exciting the second coil so asto be alternately repeated.

With this, two coils are not simultaneously excited, and the maximumvalue of the current consumption can be suppressed to a low level.Therefore, the high-speed drive based on the rotational drive by 360°per step can be performed even when a power source condition is strict,for example, when the outside temperature is low or in a state in whichthe power supply voltage is lowered.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the electronic watch further includes: adetection pulse generation circuit configured to generate a detectionpulse for detecting rotation of the rotor; and a rotation detectiondetermination circuit configured to determine rotation or non-rotationof the rotor based on a detection signal detected by applying thedetection pulse to the first coil or the second coil, and that theelectronic watch has a variable drive pulse formed of apart of theplurality of drive pulses included in the drive pulse train, and thevariable drive pulse has a length changed depending on a result ofdetermining the rotation or non-rotation of the rotor by the rotationdetection determination circuit.

With this, the rotation or non-rotation of the rotor can be detected inthe case of performing the rotational drive by 360° in one step, and itis possible to reliably rotate the rotor by outputting the correctionpulse in the case of the non-rotation. Further, the length of thehigh-speed drive pulse train to be output is only required to be alength required for rotating the rotor. Therefore, the power consumptionis reduced, and a dead time is eliminated to enable the high-speeddrive.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the drive pulse train has a duty cycleto be switched based on at least any one of a power supply voltage or atemperature.

With this, a plurality of kinds of drive pulses different in powerconsumption and output can be applied to the stepper motor.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the drive pulse train has the duty cycleto be further changed based on an elapsed time from a start of therotation.

With this, useless power consumption is reduced when the drive force issufficient, while useless power consumption caused in the case of thenon-rotation is suppressed when the drive force is insufficient, tothereby be able to achieve reduction in power consumption and the stablerotation of the rotor with a satisfactory balance.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the electronic watch has a first drivepulse train for simultaneously exciting the first coil and the secondcoil and a second drive pulse train for avoiding simultaneously excitingthe first coil and the second coil, and that the electronic watch isconfigured to select which one of the first drive pulse train and thesecond drive pulse train is to be used as the drive pulse train based onat least any one of a power supply voltage or a temperature.

With this, a current value is suppressed to suppress reduction in powersupply voltage under a condition that causes a fear that a voltage maybe temporarily lowered due to large current consumption, while it ispossible to achieve a high-speed rotational drive by 360° per step undera condition with no such fear.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the variable drive pulse includes thedrive pulse train for avoiding simultaneously exciting the first coiland the second coil, that the electronic watch has, as fixed drivepulses formed of remaining drive pulses of the plurality of drive pulsesincluded in the drive pulse train, a first fixed drive pulse forsimultaneously exciting the first coil and the second coil and a secondfixed drive pulse for avoiding simultaneously exciting the first coiland the second coil, and that the variable drive pulse is to be usedirrespective of a condition, and which one of the first fixed drivepulse and the second fixed drive pulse is to be used as the fixed drivepulse is selected based on an elapsed time from a start of the rotation.

With this, only by detecting the timing for the rotation detectionwithout directly detecting the value of the power supply voltage and thetemperature of the electronic watch, it is possible to determine thecondition in which temporary reduction in power supply voltage becomes aproblem, to thereby avoid a problem of the temporary reduction in powersupply voltage due to the large current consumption, while it ispossible to achieve a stable high-speed rotation by 360° per step.Therefore, it is possible to achieve miniaturization and reduction incost.

Further, the electronic watch according to one embodiment of the presentinvention has a feature in that the variable drive pulse includes thedrive pulse train for avoiding simultaneously exciting the first coiland the second coil, that the electronic watch has: a fixed drive pulseformed of a remaining drive pulse of the plurality of drive pulsesincluded in the drive pulse train; and a second variable drive pulse tobe applied to a coil different from a coil to which the variable drivepulse is to be applied, and that the variable drive pulse is to be usedirrespective of a condition, and which one of the fixed drive pulse andthe second variable drive pulse is to be used is selected based on anelapsed time from a start of the rotation.

With this, only by detecting the timing for the rotation detectionwithout directly detecting the value of the power supply voltage and thetemperature of the electronic watch, it is possible to determine thecondition in which temporary reduction in power supply voltage becomes aproblem, to thereby avoid a problem of the temporary reduction in powersupply voltage due to the large current consumption, while it ispossible to achieve a stable high-speed rotation by 360° per step.

Advantageous Effects of Invention

As described above, according to one embodiment the present invention,the rotational drive in increments of 360° per step is enabled by adrive pulse train formed of a plurality of drive pulses, to thereby beable to achieve the high-speed drive of the stepper motor. In addition,the rotor is rotated by one revolution for a short period of timewithout stopping, and hence the movement of the hands becomes smoother,to thereby be able to provide an electronic watch having satisfactoryappearance without awkwardness. Further, the stepper motor is driven inincrements of 360° per step, and hence a gear speed reduction ratio canbe doubled compared with the related-art rotation by 180° per step forthe stepper motor, and the torque of the hands can be increased, whichimproves the impact resistance of the hands.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram for illustrating a schematicconfiguration of an electronic watch according to a first embodiment ofthe present invention.

FIG. 2 is a plan view for illustrating a schematic configuration of atwo-coil stepper motor in the first embodiment of the present invention.

FIG. 3 is a circuit diagram for illustrating an example of a drivercircuit in the first embodiment of the present invention.

FIG. 4 are a waveform diagram of a drive pulse, an operation table fortransistors in the driver circuit, and operation diagrams of a steppermotor, for illustrating a first step of related-art rotational drive by180° per step.

FIG. 5 are a waveform diagram of a drive pulse for illustrating a secondstep of the related-art rotational drive by 180° per step and operationdiagrams of the stepper motor.

FIG. 6 are a waveform diagram of a high-speed drive pulse train and anoperation table for transistors in the driver circuit in the firstembodiment of the present invention.

FIG. 7 are operation diagrams for illustrating rotational drive by 360°per step of the two-coil stepper motor in the first embodiment of thepresent invention.

FIG. 8 is a configuration diagram for illustrating a schematicconfiguration of an electronic watch according to a second embodiment ofthe present invention.

FIG. 9 is a circuit diagram for illustrating an example of a drivercircuit in the second embodiment of the present invention.

FIG. 10 are waveform diagrams for illustrating a high-speed drive pulseand a normal drive pulse in the second embodiment of the presentinvention.

FIG. 11 is an operation table for transistors in the driver circuit interms of high-speed drive and normal drive in the second embodiment ofthe present invention.

FIG. 12 is a configuration diagram for illustrating a schematicconfiguration of an electronic watch according to a third embodiment ofthe present invention.

FIG. 13 are a waveform diagram and operation diagrams of high-speeddrive of a related-art two-coil stepper motor.

FIG. 14 are a waveform diagram of high-speed drive pulses and operationdiagrams of high-speed drive of a two-coil stepper motor in the thirdembodiment of the present invention.

FIG. 15 are a waveform diagram of high-speed drive pulses and operationdiagrams of high-speed drive of a two-coil stepper motor in ModificationExample 1 of the third embodiment of the present invention.

FIG. 16 are a waveform diagram of high-speed drive pulses and operationdiagrams of high-speed drive of a two-coil stepper motor in ModificationExample 2 of the third embodiment of the present invention.

FIG. 17 are a waveform diagram of high-speed drive pulses and operationdiagrams of high-speed drive of a two-coil stepper motor in ModificationExample 3 of the third embodiment of the present invention.

FIG. 18 is a configuration diagram for illustrating a schematicconfiguration of an electronic watch according to a fourth embodiment ofthe present invention.

FIG. 19 is a circuit diagram for illustrating an example of a drivercircuit in the fourth embodiment of the present invention.

FIG. 20 are a waveform diagram of a high-speed drive pulse train and anoperation table for transistors in the driver circuit in the fourthembodiment of the present invention.

FIG. 21 are a waveform diagram of a high-speed drive pulse train and anoperation table for transistors in the driver circuit in a fifthembodiment of the present invention.

FIG. 22 are operation diagrams for illustrating rotational drive by 360°per step of a two-coil stepper motor in the fifth embodiment of thepresent invention.

FIG. 23 is a configuration diagram for illustrating a schematicconfiguration of an electronic watch according to a sixth embodiment ofthe present invention.

FIG. 24 is a circuit diagram for illustrating an example of a drivercircuit in the sixth embodiment of the present invention.

FIG. 25 is a diagram for illustrating a structure of the stepper motor.

FIG. 26 are diagrams for illustrating the rotation and non-rotation ofthe rotor of the stepper motor.

FIG. 27 is a waveform diagram of a high-speed drive pulse train in thesixth embodiment of the present invention.

FIG. 28 is a diagram for illustrating pulse waveforms in the sixthembodiment of the present invention.

FIG. 29 is a flow chart for illustrating an operation for high-speeddrive pulse train output in the sixth embodiment of the presentinvention.

FIG. 30 is a diagram for illustrating waveforms of induced currentsgenerated in a coil A and a coil B when a variable drive pulse isapplied and illustrating pulses applied to coil terminals and detectionsignals.

FIG. 31 is a diagram for illustrating pulse waveforms in ModificationExample 1 of the sixth embodiment of the present invention.

FIG. 32 is a diagram for illustrating pulse waveforms in ModificationExample 2 of the sixth embodiment of the present invention.

FIG. 33 is a waveform diagram of a high-speed drive pulse train in aseventh embodiment of the present invention.

FIG. 34 are operation diagrams for illustrating rotational drive by 360°per step of a two-coil stepper motor in the seventh embodiment of thepresent invention.

FIG. 35 is a flow chart for illustrating an operation for high-speeddrive pulse train output in an eighth embodiment of the presentinvention.

FIG. 36 is a diagram for illustrating pulse waveforms in the eighthembodiment of the present invention.

FIG. 37 is a flow chart for illustrating an operation for high-speeddrive pulse train output in a modification example of the eighthembodiment of the present invention.

FIG. 38 is a diagram for illustrating pulse waveforms in themodification example of the eighth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the present invention are described in detail withreference to the accompanying drawings.

[Features of Respective Embodiments]

A feature of a first embodiment of the present invention resides inhaving a basic configuration of the present invention, which includesone two-coil stepper motor, and in which the two-coil stepper motor isrotated by 360° per step to move a second hand of an electronic watch byone second in one step. A feature of a second embodiment of the presentinvention resides in having a configuration including two two-coilstepper motors for minute-hour hand drive and for second hand drive, inwhich the two-coil stepper motor for the minute-hour hand drive isrotated by 360° per step to move a minute hand of the electronic watchby one minute in one step, and in which the two-coil stepper motor forthe second hand drive is rotated by 180° per step to move the secondhand of the electronic watch by one second in one step. A feature of athird embodiment of the present invention resides in having aconfiguration including one two-coil stepper motor and two drive pulsegeneration circuits, namely, a high-speed drive pulse generation circuitand a normal drive pulse generation circuit.

First Embodiment

[Description of Configuration of Electronic Watch According to FirstEmbodiment: FIG. 1]

A schematic configuration of an electronic watch according to the firstembodiment is described with reference to FIG. 1. Reference symbol 1denotes an analog indication-type electronic watch according to thefirst embodiment. The electronic watch includes an oscillation circuit 2configured to output a predetermined reference signal P1 through use ofa quartz crystal unit (not shown), a control circuit 3 configured toreceive as input the reference signal P1 to output a control signal CN1,a high-speed drive pulse generation circuit 4, a driver circuit 10, anda two-coil stepper motor 20 (hereinafter referred to as “stepper motor20”).

The electronic watch 1 includes an indication part including hands and adial, a wheel train, a power source, and an operation member, butillustration thereof is omitted because those components do not directlyrelate to the present invention.

The high-speed drive pulse generation circuit 4 receives the controlsignal CN1 as input from the control circuit 3 to generate a high-speeddrive pulse train SP10, which is formed of a plurality of high-speeddrive pulses, for driving the stepper motor 20, and output thehigh-speed drive pulse train SP10 to the driver circuit 10. Thehigh-speed drive pulse train SP10 is composed of, for example, four bitsin order to control four buffer circuits of the driver circuit 10, whichare described later, to output drive waveforms O1 to O4.

The high-speed drive pulse train SP10 is a drive pulse for rotating thestepper motor 20 in increments of 360° per step, but cannot always drivethe hands at high speed depending on a gear speed reduction ratio of thewheel train for moving the hands. However, the high-speed drive pulsetrain SP10 is a drive pulse that enables the high-speed drive, and istherefore referred to as “high-speed drive pulse train”.

The driver circuit 10 receives the high-speed drive pulse train SP10 asinput to supply the drive waveforms O1, O2, O3, and O4 that are based ona plurality of drive pulses to the stepper motor 20, to thereby drivethe stepper motor 20. A detailed configuration of the driver circuit 10is described later.

The stepper motor 20 includes two coils, namely, a coil A and a coil B.Details of the stepper motor 20 are described later.

[Description of Configuration of Stepper Motor: FIG. 2]

Next, the configuration of the stepper motor 20 is described. Thestepper motor 20 includes a rotor 21, a stator 22, and the two coils Aand B. The rotor 21 is a disc-shaped rotary member magnetized into twopoles, and is magnetized to an S-pole and an N-pole in a radialdirection of the rotor 21.

The stator 22 is made of a soft magnetic material, and has a rotor hole22 d for allowing the rotor 21 to be inserted therethrough. The rotor 21is arranged in this rotor hole 22 d. The stator 22 includes a firststator magnetic-pole portion 22 a (hereinafter abbreviated as “firstmagnetic-pole portion 22 a”) and a second stator magnetic-pole portion22 b (hereinafter abbreviated as “second magnetic-pole portion 22 b”),which are formed so as to substantially oppose to each other through therotor 21. Further, the stator 22 includes a third stator magnetic-poleportion 22 c (hereinafter abbreviated as “third magnetic-pole portion 22c”) formed at a position between the first magnetic-pole portion 22 aand the second magnetic-pole portion 22 b so as to face the rotor 21.

In addition, the coil A is provided as a first coil to be magneticallycoupled to the first magnetic-pole portion 22 a and the thirdmagnetic-pole portion 22 c, and the coil B is provided as a second coilto be magnetically coupled to the second magnetic-pole portion 22 b andthe third magnetic-pole portion 22 c.

The coil A includes coil terminals O1 and O2 on an insulating substrate23 a, and both ends of winding of the coil A are connected to the coilterminals O1 and O2. Further, the coil B includes coil terminals O3 andO4 on an insulating substrate 23 b, and both ends of winding of the coilB are connected to the coil terminals O3 and O4. The above-mentioneddrive waveforms O1 to O4 output from the driver circuit 20 are suppliedto the coil terminals O1 to O4, respectively.

For easy understanding of the description, the same reference symbol isused for each coil terminal and each drive waveform to be suppliedthereto. Further, for example, winding of the coil A is started at thecoil terminal O1, and winding of the coil B is started at the coilterminal O4.

The rotor 21 illustrated in FIG. 2 is in a stationary state. The upperside of FIG. 2 is defined as 0°, and 90°, 180°, and 270° are definedfrom that position in a counterclockwise direction. When the N-pole ofthe rotor 21 is positioned at 0° and at 180°, the rotor 21 is at astationary position (statically stable point). Thus, the rotor 21illustrated in FIG. 2 is at the stationary position with the N-polebeing positioned at 0°.

[Description of Circuit Configuration of Driver Circuit: FIG. 3]

Next, an example of the circuit configuration of the driver circuit 10configured to drive the stepper motor 20 is described with reference toFIG. 3. The driver circuit 10 includes four buffer circuits configuredto supply the drive waveforms O1 and O2 and the drive waveforms O3 andO4 caused by the high-speed drive pulse train SP10 to the coil A and thecoil B of the stepper motor 20, respectively.

Now, the configuration of those four buffer circuits is described.First, a buffer circuit including a transistor P1 being a P-channel MOStransistor having a low ON resistance and a transistor N1 being anN-channel MOS transistor having a low ON resistance, which arecomplementarily connected to each other, outputs the drive waveform O1to be supplied to the coil terminal O1 of the coil A.

Further, similarly, a buffer circuit including a transistor P2 and atransistor N2 each having a low ON resistance, which are complementarilyconnected to each other, outputs the drive waveform O2 to be supplied tothe coil terminal O2 of the coil A.

Further, similarly, a buffer circuit including a transistor P3 and atransistor N3 each having a low ON resistance, which are complementarilyconnected to each other, outputs the drive waveform O3 to be supplied tothe coil terminal O3 of the coil B.

Further, similarly, a buffer circuit including a transistor P4 and atransistor N4 each having a low ON resistance, which are complementarilyconnected to each other, outputs the drive waveform O4 to be supplied tothe coil terminal O4 of the coil B.

Although not shown, each of gate terminals G of the respectivetransistors P1 to P4 and N1 to N4 receives the high-speed drive pulsetrain SP10 output from the above-mentioned high-speed drive pulsegeneration circuit 4 as input, and each of the transistors is ON/OFFcontrolled based on the high-speed drive pulse train SP10 to output thedrive waveforms O1 to O4. In this case, when the high-speed drive pulsetrain SP10 is composed of four bits as described above, although notshown, the high-speed drive pulse train SP10 of each of the bits isinput to each of the gate terminals G of the transistors of the fourbuffer circuits. Details of the ON/OFF operation of each of thetransistors are described later.

[Description of Drive of Related-Art Two-Coil Stepper Motor: FIG. 4 andFIGS. 5]

Next, a drive waveform for rotationally driving the two-coil steppermotor in increments of 180° per step is known, but is required forunderstanding the present invention, and hence an example of therelated-art drive waveform for performing rotational drive by 180° perstep in two steps to perform rotational drive by 360° and the outline ofthe rotational operation of a related-art stepper motor are describedwith reference to FIG. 4 and FIG. 5 through use of the stepper motor 20illustrated in FIG. 2 and the driver circuit 10 of FIG. 3.

First, with reference to FIG. 4, description is given of a drive pulseSP01 in a first step for rotating the N-pole of the rotor 21 of thestepper motor 20 from the stationary position of 0° (see FIG. 2) in theforward rotation direction (counterclockwise) by 180° and the rotationaloperation of the rotor 21.

FIG. 4(a) is an illustration of a drive waveform based on the drivepulse SP01 for rotating the N-pole of the rotor 21 of the stepper motor20 from the stationary position of 0° in the forward direction by 180°in one step, and the drive waveforms O1 to O4 output from the drivercircuit 10 are illustrated. In this case, the drive waveforms O1 to O4are maintained at a voltage of 0 V (VDD) in a normal state, and changedto have a voltage of less than 0 V (VSS) due to the drive pulse. Thedisplay forms of the drive waveforms O1 to O4 are used for all the drivewaveforms described later in common.

FIG. 4(b) is an operation table (ON/OFF operation) for each of thetransistors in the driver circuit 10 to be operated based on the drivepulse SP01 in the first step and a drive pulse SP02 in a second step,which is described later, of the stepper motor 20. FIG. 4(c) and FIG.4(d) are illustrations of the rotational operation of the stepper motor20 based on the drive pulse SP01 in the first step.

In FIG. 4(a), when the N-pole of the rotor 21 is rotated from thestationary position of 0° in the forward direction in the first step,the drive waveform O3 is changed to have a voltage of less than 0 V dueto the drive pulse SP01, and the other drive waveforms O1, O2, and O4are changed to have a voltage of 0 V. Further, when the output of thedrive pulse SP01 is ended, all the drive waveforms O1 to O4 aremaintained at a voltage of 0 V until the arrival of the next drivepulse.

Next, with reference to the operation table of FIG. 4(b), description isgiven of the operation of each of the transistors of the driver circuit10 due to the drive pulse SP01 in the first step. In this case, thedrive waveform O3 is changed to have a voltage of less than 0 V due tothe drive pulse SP01, which turns on the transistor N3 and thetransistors P4 of the driver circuit 10 and turns off the transistor P3and the transistor N4, and hence a drive current flows from the coilterminal O4 into the coil terminal O3 to excite the coil B.

Further, the drive waveforms O1 and O2 output from the driver circuit 10are both changed to have a voltage of 0 V due to the drive pulse SP01 inthe first step, which turns on the transistors P1 and P2 and turns offthe transistors N1 and N2. The coil terminals O1 and O2 of the coil Aare both connected to VDD to be changed to have a voltage of 0 V, and adrive current is not caused to flow into the coil A, which inhibits thecoil A from being excited.

Next, with reference to FIG. 4(c) and FIG. 4(d), description is given ofthe rotational operation of the stepper motor 20 in the first step. InFIG. 4(c), when the drive waveform O3 is changed to have a voltage ofless than 0 V due to the drive pulse SP01, as described above, althoughnot shown, a drive current flows from the coil terminal O4 into the coilterminal O3 to excite the coil B (the arrow in the coil B indicates theexcitation direction). With this, the second magnetic-pole portion 22 bis magnetized to the N-pole, and the third magnetic-pole portion 22 c ismagnetized to the S-pole. In addition, the coil A is inhibited frombeing excited. Thus, the first magnetic-pole portion 22 a has the S-polein the same manner as the third magnetic-pole portion 22 c.

As a result, the N-pole of the rotor 21 and the S-poles of the firstmagnetic-pole portion 22 a and the third magnetic-pole portion 22 cattract each other, while the S-pole of the rotor 21 and the N-pole ofthe second magnetic-pole portion 22 b attract each other. Thus, therotor 21 is rotated from the stationary position of 0° in thecounterclockwise direction by about 135°.

Next, in FIG. 4(d), when the drive pulse SP01 is ended, the coil B stopsbeing excited, which cancels the magnetization of the first to thirdmagnetic-pole portions 22 a to 22 c, but the rotor 21 continues torotate until the N-pole moves from the position of about 135° to reachthe statically stable point of 180°, and is held at that position. As aresult, the rotor 21 is rotationally driven by 180° due to the drivepulse SP01 in the first step.

Next, with reference to FIG. 5, description is given of the drive pulseSP02 in the second step for rotating the N-pole of the rotor 21 of thestepper motor 20 from the stationary position of 180° in the forwarddirection (counterclockwise) and the rotational operation of the rotor21. FIG. 5(a) is an illustration of a drive waveform based on the drivepulse SP02 for rotating the N-pole of the rotor 21 of the stepper motor20 from the stationary position of 180° in the forward direction by 180°in one step, and the drive waveforms O1 to O4 output from the drivercircuit 10 are illustrated. FIG. 5(b) to FIG. 5(d) are illustrations ofthe rotational operation of the stepper motor 20 based on the drivepulse SP02 in the second step.

In FIG. 5(a), when the N-pole of the rotor 21 is rotated from thestationary position of 180° in the forward direction in the second step,the drive waveform O4 is changed to have a voltage of less than 0 V dueto the drive pulse SP02, and the other drive waveforms O1, O2, and O3are changed to have a voltage of 0 V. Further, when the output of thedrive pulse SP02 is ended, all the drive waveforms O1 to O4 aremaintained at a voltage of 0 V until the arrival of the next drivepulse.

Next, with reference to the operation table of FIG. 4(b), description isgiven of the operation of each of the transistors of the driver circuit10 due to the drive pulse SP02 in the second step. In this case, thedrive waveform O4 is changed to have a voltage of less than 0 V due tothe drive pulse SP02, which turns on the transistor N4 and thetransistors P3 of the driver circuit 10 and turns off the transistor P4and the transistor N3, and hence a drive current flows from the coilterminal O3 into the coil terminal O4 to excite the coil B in adirection reverse to that of the first step.

Further, similarly to the first step, the drive waveforms O1 and O2 areboth changed to have a voltage of 0 V due to the drive pulse SP02 in thesecond step, which turns on the transistors P1 and P2 and turns off thetransistors N1 and N2. The coil terminals O1 and O2 of the coil A areboth connected to VDD to be changed to have a voltage of 0 V, and adrive current is not caused to flow into the coil A, which inhibits thecoil A from being excited.

Next, with reference to FIG. 5(b) to FIG. 5(d), description is given ofthe rotational operation of the stepper motor 20 in the second step.FIG. 5(b) indicates the initial position of the rotor 21 in the secondstep, and is an illustration of a state in which the N-pole of the rotor21 is located at the stationary position of 180° (downward direction onthe figure) and is held.

After this state, in FIG. 5(c), when the drive waveform O4 is changed tohave a voltage of less than 0 V due to the drive pulse SP02, asdescribed above, although not shown, a drive current flows from the coilterminal O3 into the coil terminal O4 to excite the coil B (the arrow inthe coil B indicates the excitation direction). With this, the secondmagnetic-pole portion 22 b is magnetized to the S-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the N-pole. In addition, thecoil A is inhibited from being excited. Thus, the first magnetic-poleportion 22 a has the N-pole in the same manner as the thirdmagnetic-pole portion 22 c.

As a result, the S-pole of the rotor 21 and the N-poles of the firstmagnetic-pole portion 22 a and the third magnetic-pole portion 22 cattract each other, while the N-pole of the rotor 21 and the S-pole ofthe second magnetic-pole portion 22 b attract each other. Thus, therotor 21 is rotated from the stationary position of 180° in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom 0° to the position of about 315°.

Next, in FIG. 5(d), when the drive pulse SP02 is ended, the coil B stopsbeing excited, which cancels the magnetization of the first to thirdmagnetic-pole portions 22 a to 22 c, but the rotor 21 continues torotate until the N-pole moves from the position of about 315° to reachthe statically stable point of 0°, and is held at that position. As aresult, the rotor 21 is rotationally driven by 180° due to the drivepulse SP02 in the second step.

In this manner, the related-art two-coil stepper motor is normallyrotationally driven in increments of 180° per step due to a one-shotdrive pulse, and accordingly is rotationally driven by 360° in twosteps. In this rotational drive by 360° in two steps, there is a timeinterval between the drive pulse SP01 in the first step and the drivepulse SP02 in the second step. Even with the two-coil stepper motor, asdescribed above, there occur, for example, deceleration, vibration,stop, and reacceleration in the movement of the rotor 21, and the handsmove in an awkward and unnatural manner to exhibit lack in smoothnessand poor-looking movement, which causes a problem.

[Description of High-Speed Drive Pulse and Operation of Each Transistorof Driver Circuit in First Embodiment: FIGS. 6]

Next, with reference to FIG. 6, description is given of an example ofthe drive waveform of a high-speed drive pulse for rotationally drivingthe stepper motor in the first embodiment in increments of 360° per stepand the operation of each of the transistors of the driver circuit.

First, with reference to FIG. 6(a), description is given of the drivewaveform of the high-speed drive pulse train SP10 for rotationallydriving the N-pole of the rotor 21 of the stepper motor 20 from thestationary position of 0° (see FIG. 2) in the forward rotation direction(counterclockwise) in increments of 360°. FIG. 6(a) is an illustrationof a drive waveform based on the high-speed drive pulse train SP10 forrotating the rotor 21 of the stepper motor 20 in increments of 360° perstep and an example of the four drive waveforms O1 to O4 to be outputfrom the driver circuit 10.

In FIG. 6(a), the high-speed drive pulse train SP10 is formed of threedrive pulses, namely, a first drive pulse SP11, a second drive pulseSP12, and a third drive pulse SP13 so as to be output sequentially.

In the first drive pulse SP11, the drive waveform O3 has a voltage ofless than 0 V, and the other drive waveforms O1, O2, and O4 have avoltage of 0 V. With this, a drive current flows into the coil B of thestepper motor 20 connected to the drive waveforms O3 and O4 to excitethe coil B.

Further, in the second drive pulse SP12, the drive waveforms O2 and O4have a voltage of less than 0 V, and the drive waveforms O1 and O3 havea voltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20 to excite both the coil A and thecoil B.

Further, in the third drive pulse SP13, the drive waveform O4 has avoltage of less than 0 V, and the other drive waveforms O1, O2, and O3have a voltage of 0 V. With this, the coil B of the stepper motor 20 isexcited in the same direction as in the case of the second drive pulseSP12.

A cycle period of the high-speed drive pulse train SP10, namely, a totalsum of the pulse widths of the first to third drive pulses SP11 to SP13is freely set. Each of the drive waveforms O1 to O4 is illustrated asthat of a continuous full pulse, but may be that of a chopper-shapedrive pulse based on a plurality of minute pulse groups.

Next, with reference to the operation table of FIG. 6(b), description isgiven of the operation of each of the transistors of the driver circuit10 based on the high-speed drive pulse train SP10. In regard to thedriver circuit 10, FIG. 3 is referred to. In FIG. 6(b), in the firstdrive pulse SP11, the drive waveform O3 has a voltage of less than 0 V,and the drive waveform O4 has a voltage of 0 V. Thus, the transistor N3and the transistor P4 are turned on, while the transistor P3 and thetransistor N4 are turned off, and a drive current flows from the coilterminal O4 of the coil B into the coil terminal O3 to excite the coilB.

Further, the drive waveforms O1 and O2 both have a voltage of 0 V, andhence the transistors P1 and P2 are turned on, while the transistors N1and N2 are turned off. Thus, a drive current is not caused to flow intothe coil A, which inhibits the coil A from being excited.

Further, in the second drive pulse SP12, the drive waveform O1 has avoltage of 0 V, and the drive waveform O2 has a voltage of less than 0V. Thus, the transistor P1 and the transistor N2 are turned on, and thetransistor N1 and the transistor P2 are turned off, which causes a drivecurrent to flow from the coil terminal O1 to the coil terminal O2 toexcite the coil A. Further, the drive waveform O3 has a voltage of 0 V,and the drive waveform O4 has a voltage of less than 0 V. Thus, thetransistor P3 and the transistor N4 are turned on, and the transistor N3and the transistor P4 are turned off, which causes a drive current toflow from the coil terminal O3 into the coil terminal O4 to excite thecoil B.

Further, in the third drive pulse SP13, the drive waveform O3 has avoltage of 0 V, and the drive waveform O4 has a voltage of less than 0V. Thus, the transistor P3 and the transistor N4 are turned on, and thetransistor N3 and the transistor P4 are turned off, which causes a drivecurrent to flow from the coil terminal O3 to the coil terminal O4 toexcite the coil B. Further, the drive waveforms O1 and O2 both have avoltage of 0 V. Thus, the transistor P1 and P2 are turned on, thetransistor N1 and N2 are turned off, and a drive current is not causedto flow into the coil A, which inhibits the coil A from being excited.

In this manner, each of the transistors of the driver circuit 10 isON/OFF controlled based on the three drive pulses, namely, the first tothird drive pulses SP11 to SP13 of the high-speed drive pulse trainSP10, to thereby excite the coils A and B of the stepper motor 20.

[Description of Rotational Drive by 360° Per Step in First Embodiment:FIGS. 7]

Next, with reference to FIG. 7, description is given of the high-speedrotational drive of the stepper motor 20 in increments of 360° per stepin the first embodiment. As conditions of the description, it is assumedthat the drive pulse is the high-speed drive pulse train SP10illustrated and shown in FIG. 6, and the N-pole of the rotor 21 islocated at the stationary position of 0° in the initial state of thestepper motor 20 as illustrated in FIG. 2 referred to above. Further,the reference symbols of the respective members of the stepper motor 20are written only in FIG. 7(a) and omitted in the other figures.

FIG. 7(a) is an illustration of a state in which the first drive pulseSP11 of the high-speed drive pulse train SP10 is supplied to the steppermotor 20. In this case, as described above, a drive current (not shown)flows from the coil terminal O4 into the coil terminal O3 to excite thecoil B in the direction indicated by the arrow. With this, the secondmagnetic-pole portion 22 b is magnetized to the N-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the S-pole. In addition, thecoil A is inhibited from being excited. Thus, the first magnetic-poleportion 22 a has the S-pole in the same manner as the thirdmagnetic-pole portion 22 c.

As a result, the N-pole of the rotor 21 and the S-poles of the firstmagnetic-pole portion 22 a and the third magnetic-pole portion 22 cattract each other, while the S-pole of the rotor 21 and the N-pole ofthe second magnetic-pole portion 22 b attract each other. Thus, therotor 21 is rotated in the counterclockwise direction, and the N-pole ofthe rotor 21 is rotated from the stationary position of 0° to theposition of about 135°.

Next, in FIG. 7(b), when the second drive pulse SP12 is supplied, asdescribed above, a drive current (not shown) flows from the coilterminal O1 into the coil terminal O2 to excite the coil A in thedirection indicated by the arrow. Further, similarly, a drive current(not shown) flows from the coil terminal O3 into the coil terminal O4 toexcite the coil B in the direction indicated by the arrow (directionreverse to that of the coil A).

With this, the first magnetic-pole portion 22 a is magnetized to theN-pole, the second magnetic-pole portion 22 b is magnetized to theS-pole, and the third magnetic-pole portion 22 c is not magnetized dueto canceled magnetization. As a result, the N-pole of the rotor 21 andthe S-pole of the second magnetic-pole portion 22 b attract each other,while the S-pole of the rotor 21 and the N-pole of the firstmagnetic-pole portion 22 a attract each other. Thus, the rotor 21 isfurther rotated in the counterclockwise direction without stopping, andthe N-pole of the rotor 21 is rotated to reach the position of about270°.

Next, in FIG. 7(c), when the second drive pulse SP13 is supplied, asdescribed above, a drive current (not shown) flows from the coilterminal O3 into the coil terminal O4 to excite the coil B in thedirection indicated by the arrow. With this, the second magnetic-poleportion 22 b is magnetized to the S-pole, and the third magnetic-poleportion 22 c is magnetized to the N-pole. In addition, the coil A isinhibited from being excited. Thus, the first magnetic-pole portion 22 ahas the N-pole in the same manner as the third magnetic-pole portion 22c. As a result, the S-pole of the rotor 21 and the N-poles of the firstmagnetic-pole portion 22 a and the third magnetic-pole portion 22 cattract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction without stopping, and the N-pole of the rotor21 is rotated to reach the position of about 315°.

Next, in FIG. 7(d), when the supply of the high-speed drive pulse trainSP10 is ended, the drive waveforms O1 to O4 all have a voltage of 0 V.Thus, the coil A and the coil B of the stepper motor 20 stop beingexcited, which cancels the magnetization of the first to thirdmagnetic-pole portions 22 a to 22 c, but the rotor 21 continues torotate until the N-pole moves from the position of about 315° to reachthe statically stable point of) 360° (0°) without stopping, and is heldat that position. In this manner, the stepper motor 20 is rotationallydriven by 360° through one-step drive based on the high-speed drivepulse train SP10 formed of the three drive pulses SP11 to SP13. That is,it is possible to achieve the rotational drive in increments of 360° perstep.

As described above, with the electronic watch according to the firstembodiment, it is possible to perform the rotational drive in incrementsof 360° in one step by supplying the high-speed drive pulse train SP10formed of the three drive pulses SP11 to SP13 to the stepper motor 20.With this, although the hands are hitherto moved for one second with thegear speed reduction ratio of the wheel train being set to 1/30 in therotation by 180° per step, in the first embodiment, the stepper motor isdriven to be rotated by 360° per step, which enables the hands to bemoved for one second with the gear speed reduction ratio being double to1/60, and an increase in torque of the hands can be achieved, to therebygreatly increase the impact resistance of the hands.

Further, the rotor 21 is rotated in increments of 360° without stoppingduring the rotation, and hence the movement of the hands becomessmoother, to thereby be able to provide an electronic watch havingsatisfactory appearance without awkwardness. Further, the stepper motoris rotated by 360° per step, to thereby be able to alleviate thedeviation of the position indicated by the hands due to a backlash ofthe wheel train or the like.

When the N-pole of the rotor 21 of the stepper motor 20 is located atthe stationary position of 0° (see FIG. 2), in order to rotate the rotor21 reversely (in the clockwise direction) by 360° per step, although notshown, the stepper motor 20 is driven with the drive waveforms O1 and O4being exchanged to each other and the drive waveforms O2 and O3 beingexchanged to each other in the drive waveforms O1 to O4 illustrated inFIG. 6(a), to thereby be able to reversely rotate the rotor 21. Also inthis reverse drive, the rotor 21 can be rotated in increments of 360°per step, and hence is possible to obtain the same effects.

Further, when the N-pole of the rotor 21 of the stepper motor 20 islocated at the stationary position of 180° (S-pole is at 0°), the rotor21 can be similarly driven in increments of 360° per step with the drivewaveforms O1 and O2 being exchanged to each other and the drivewaveforms O3 and O4 being exchanged to each other in the drive waveformsO1 to O4 illustrated in FIG. 6(a).

Second Embodiment

[Description of Configuration of Electronic Watch According to SecondEmbodiment: FIG. 8]

Next, a schematic configuration of an electronic watch according to thesecond embodiment is described with reference to FIG. 8. Referencesymbol 30 denotes an analog indication-type electronic watch accordingto the second embodiment. The electronic watch 30 includes anoscillation circuit 32 configured to output the predetermined referencesignal P1 through use of a quartz crystal unit (not shown), a controlcircuit 33 configured to receive as input the reference signal P1 tooutput control signals CN1, CN2, and CN3, a high-speed drive pulsegeneration circuit 34, a minute-hour hand drive timing circuit 35, asecond hand drive timing circuit 36, a selector 37, a driver circuit 40,a first two-coil stepper motor 41 (hereinafter abbreviated as “steppermotor 41”), and a second two-coil stepper motor 42 (hereinafterabbreviated as “stepper motor 42”).

The electronic watch 30 includes an indication part including hands, awheel train, a power source, and an operation member, but illustrationthereof is omitted because those components do not directly relate tothe present invention.

The high-speed drive pulse generation circuit 34 receives the controlsignal CN1 as input to generate and output a high-speed drive pulsetrain SP, which is formed of a plurality of high-speed drive pulses, fordriving the stepper motors 41 and 42.

The minute-hour hand drive timing circuit 35 receives the control signalCN2 as input, and generates and outputs a high-speed drive timing signalP2 for selecting a high-speed drive pulse for driving minute-hour hands.

The secondhand drive timing circuit 36 receives the control signal CN3as input, and generates and outputs a normal drive timing signal P3 forselecting a normal drive pulse for driving a second hand.

The selector 37 receives the high-speed drive pulse train SP as input,and passes the high-speed drive pulse train SP as it is based on thehigh-speed drive timing signal P2 to output the high-speed drive pulsetrain SP as the high-speed drive pulse train SP10. Further, the selector37 selects a specific drive pulse of the high-speed drive pulse train SPbased on the normal drive timing signal P3 to output the specific drivepulse as a normal drive pulse SP00. A case in which the high-speed drivepulse train SP10 is output is referred to as “high-speed drive mode”,and a case in which the normal drive pulse SP00 is output is referred toas “normal drive mode”.

The driver circuit 40 receives, as input, the high-speed drive pulsetrain SP10 or the normal drive pulse SP00 from the selector 37, andsupplies the drive waveforms O1 to O4 and drive waveforms O5 to O8 basedon the respective drive pulses to the coils A and the coils B of therespective two stepper motors 41 and 42, to thereby drive the steppermotors 41 and 42. A detailed configuration of the driver circuit 40 isdescribed later.

The stepper motors 41 and 42 each include the coil A and the coil B, andhave the same configuration as that of the stepper motor 20 in the firstembodiment (see FIG. 2), and hence detailed description thereof isomitted. In this case, the stepper motor 41 is arranged to drive, forexample, the minute-hour hands (not shown) of the electronic watch 30,and the stepper motor 42 is arranged to drive, for example, the secondhand (not shown) of the electronic watch 30.

The coil terminals O1 and O2 of the coil A of the stepper motor 41 areconnected to the drive waveforms O1 and O2 output from the drivercircuit 40, respectively, while the coil terminals O3 and O4 of the coilB are connected to the drive waveforms O3 and O4 output from the drivercircuit 40, respectively. Further, the coil terminals O1 and O2 of thecoil A of the other stepper motor 42 are connected to the drivewaveforms O5 and O6 output from the driver circuit 40, respectively,while the coil terminals O3 and O4 of the coil B are connected to thedrive waveforms O7 and O8 output from the driver circuit 40,respectively. In this manner, the feature of the electronic watch 30according to the second embodiment resides in including the two steppermotors 41 and 42 for the minute-hour hand drive and for the second handdrive.

[Description of Circuit Configuration of Driver Circuit in SecondEmbodiment: FIG. 9]

Next, with reference to FIG. 9, description is given of an example ofthe circuit configuration of the driver circuit 40 configured to drivethe stepper motors 41 and 42. The driver circuit 40 is formed of eightbuffer circuits configured to supply eight drive waveforms to the coilsA and the coils B of the respective stepper motors 41 and 42.

In this case, a buffer circuit including the transistor P1 being aP-channel MOS transistor having a low ON resistance and the transistorN1 being an N-channel MOS transistor having a low ON resistance, whichare complementarily connected to each other, outputs the drive waveformO1 and is connected to the coil terminal O1 of the coil A. Further,similarly, a buffer circuit including the transistor P2 and thetransistor N2 each having a low ON resistance outputs the drive waveformO2 and is connected to the coil terminal O2 of the coil A.

Further, similarly, a buffer circuit including the transistor P3 and thetransistor N3 each having a low ON resistance outputs the drive waveformO3 and is connected to the coil terminal O3 of the coil B.

Further, similarly, a buffer circuit including the transistor P4 and thetransistor N4 each having a low ON resistance outputs the drive waveformO4 and is connected to the coil terminal O4 of the coil B.

Further, for the stepper motor 42, a buffer circuit including atransistor P5 having a low ON resistance and a transistor N5 having alow ON resistance, which are complementarily connected to each other,outputs the drive waveform O5 and is connected to the coil terminal O1of the coil A.

Further, similarly, a buffer circuit including a transistor P6 and atransistor N6 each having a low ON resistance outputs the drive waveformO6 and is connected to the coil terminal O2 of the coil A.

Further, similarly, a buffer circuit including a transistor P7 and atransistor N7 each having a low ON resistance outputs the drive waveformO7 and is connected to the coil terminal O3 of the coil B.

Further, similarly, a buffer circuit including a transistor P8 and atransistor N8 each having a low ON resistance outputs the drive waveformO8 and is connected to the coil terminal O4 of the coil B.

Although not shown, each of gate terminals G of the respectivetransistors P1 to P8 and N1 to N8 receives the high-speed drive pulsetrain SP10 or the normal drive pulse SP00 output from theabove-mentioned selector 37 as input, and each of the transistors isON/OFF controlled based on the drive pulse to supply the drive waveformsO1 to O4 and the drive waveforms O5 to O8 to the coils A and the coils Bof the respective two stepper motors 41 and 42.

[Description of Generation of Drive Pulse and Drive Waveform in SecondEmbodiment: FIGS. 10]

Next, with reference to FIG. 10, description is given of an example ofthe generation of a drive pulse and a drive waveform in the secondembodiment. FIG. 10(a) is an example of the high-speed drive pulse trainSP output from the high-speed drive pulse generation circuit 34, thehigh-speed drive timing signal P2, and the normal drive timing signalP3. FIG. 10(b) is an example of the drive waveform of the high-speeddrive pulse train SP10 for driving the minute-hour hands in thehigh-speed drive mode. FIG. 10(c) is an example of the drive waveform ofthe normal drive pulse SP00 for driving the second hand in the normaldrive mode. FIG. 10(a) to FIG. 10(c) share the same time axis whendrawn. In regard to the configuration of the electronic watch 30, theconfiguration diagram of FIG. 8 is referred to.

In FIG. 10(a), the high-speed drive pulse train SP to be output from thehigh-speed drive pulse generation circuit 34 is a pulse train composedof, for example, four bits SPa to SPd and formed of three drive pulses,namely, a first drive pulse SP1, a second drive pulse SP2, and a thirddrive pulse SP3 in time series, which includes a logical “1” or alogical “0” in order to ON/OFF control each of the transistors of thedriver circuit 40.

In the first drive pulse SP1, SPa, SPb, and SPd are a logical “1”, andSPc is a logical “0”. Further, in the second drive pulse SP2, SPa andSPc are a logical “1”, and SPb and SPd are a logical “0”. Further, inthe third drive pulse SP3, SPa, SPb, and SPc are a logical “1”, and SPdis a logical “0”. This high-speed drive pulse train SP is repeatedlyoutput for a freely-set period at a predetermined cycle under control ofthe control circuit 33, and it is indicated in FIG. 10(a) that theoutput is repeated at least two times.

Further, the high-speed drive timing signal P2 is a signal indicating,for example, a logical “0” at the timing of the first to third drivepulses SP1 to SP3 of the high-speed drive pulse train SP and a logical“1” at another timing. In the high-speed drive mode, the selector 37passes the high-speed drive pulse train SP at the timing of the logical“0” of the high-speed drive timing signal P2, and supplies thehigh-speed drive pulse train SP to the driver circuit 40 as thehigh-speed drive pulse train SP10.

Further, the normal drive timing signal P3 is a signal having two stepsand indicating a logical “0” in accordance with the timing of the firstdrive pulse SP1 of the high-speed drive pulse train SP in the initialfirst step and a logical “0” in accordance with the timing of the thirddrive pulse SP3 in the subsequent second step. In the normal drive mode,the selector 37 passes the first drive pulse SP1 (in the first step) andthe third drive pulse SP3 (in the second step) of the high-speed drivepulse train SP at the timing of the logical “0” of the normal drivetiming signal P3, and supplies the first drive pulse SP1 and the thirddrive pulse SP3 to the driver circuit 40 as the normal drive pulse SP00.

Next, with reference to FIG. 10(b), description is given of the drivepulse in the high-speed drive mode. When the high-speed drive mode isselected, the control circuit 33 outputs the control signal CN2, and theminute-hour hand drive timing circuit 35 outputs the high-speed drivetiming signal P2 based on the control signal CN2. The selector 37operates so that the four-bit high-speed drive pulse train SP passestherethrough to be output based on the high-speed drive timing signalP2.

With this, in the high-speed drive mode, as described above, thefour-bit high-speed drive pulse train SP passes through the selector 37as it is to be supplied to the driver circuit 40 as the high-speed drivepulse train SP10. The high-speed drive pulse train SP10 output from theselector 37 is the same as the high-speed drive pulse train SP10 in thefirst embodiment, and is therefore denoted by the same reference symbol,and the first, second, and third drive pulses SP11, SP12, and SP13,which form the high-speed drive pulse train SP10, are also denoted bythe same reference symbols.

The driver circuit 40 sequentially ON/OFF operates each of thetransistors based on the first to third drive pulses SP11 to SP13 of theinput four-bit high-speed drive pulse train SP10 to output the drivewaveforms O1 to O4 illustrated in FIG. 10(b).

The coil A and the coil B of the stepper motor 41 receive those drivewaveforms O1 to O4 as input to be rotationally driven at high speed inincrements of 360° per step. The high-speed rotational drive performedby the stepper motor 41 is the same as the high-speed rotational drivein increments of 360° per step in the above-mentioned first embodiment(see FIG. 7), and hence the description of the operation of the steppermotor is omitted.

In this case, when a cycle period T1 (see FIG. 10(b)) of the high-speeddrive pulse train SP10 is set to 60 seconds and the gear speed reductionratio of the wheel train (not shown) is set large (to 1/60) so that theminute hand proceeds by one minute based on the rotation by 360° perstep of the stepper motor 41, the stepper motor 41 is rotated by 360°every 60 seconds, to thereby be able to move the minute hand by oneminute.

Next, with reference to FIG. 10(c), description is given of the drivepulse in the normal drive mode. When the normal drive mode is selected,the control circuit 33 outputs the control signal CN3, and the secondhand drive timing circuit 36 outputs the normal drive timing signal P3based on the control signal CN3. The selector 37 operates so that thefour-bit high-speed drive pulse train SP passes therethrough to beoutput during a period in which the normal drive timing signal P3 is alogical “0”.

With this, in the normal drive mode, as described above, the four-bitnormal drive pulse SP00 selected by the selector 37 is output to besupplied to the driver circuit 40. The drive pulse in the first step ofthe normal drive pulse SP00 is referred to as “first drive pulse SP01”,and the drive pulse in the second step of the normal drive pulse SP00 isreferred to as “second drive pulse SP02”.

The driver circuit 40 ON/OFF operates each of the transistors based onthe first drive pulse SP01 and the second drive pulse SP02 of the inputfour-bit normal drive pulse train SP00 to output the drive waveforms O5to O8 illustrated in FIG. 10(c).

In this case, in the first drive pulse SP01 being the first step of thenormal drive pulse SP00, the selected high-speed drive pulse train SPcindicates a logical “0” (see FIG. 10(a)), and hence the drive waveformO7 is controlled so as to have a voltage of less than 0 V, and the otherdrive waveforms O5, O6, and O8 have a voltage of 0 V. Further, in thesecond drive pulse SP02 being the second step of the normal drive pulseSP00, the selected high-speed drive pulse train SPd indicates a logical“0” (see FIG. 10(a)), the drive waveform O8 is controlled so as to havea voltage of less than 0 V, and the other drive waveforms O5, O6, and O7have a voltage of 0 V. The coil A and the coil B of the stepper motor 42receive those drive waveforms O5 to O8 as input to be subjected tonormal drive.

The drive waveforms O5 to O8 based on this normal drive pulse SP00 arethe same as the drive waveforms in the related-art rotation by 180° perstep described above with reference to FIG. 4 and FIG. 5. Thus, thenormal drive operation of the stepper motor 42 is the same as therelated-art rotational drive by 180° per step, which is illustrated andshown in FIG. 4 and FIG. 5, and hence description thereof is omittedhere.

In this manner, the normal drive pulse SP00 in the normal drive modeenables the stepper motor 42 configured to drive the second hand to berotated by 180° per step. Then, when a cycle period T2 (FIG. 10(c))between the first drive pulse SP01 and the second drive pulse SP02 isset to, for example, one second, the stepper motor 42 is rotated by 180°every second, to thereby be able to move the second hand by one second.That is, in the second embodiment, the minute hand is moved by oneminute by subjecting the stepper motor 41 to the rotational drive by360° per step due to the high-speed drive pulse train SP10 in thehigh-speed drive mode, while in the normal drive mode, the second handis moved by one second by subjecting the stepper motor 42 to therotational drive by 180° per step due to the normal drive pulse SP00 asin the related art.

The drive waveforms O1 to O4 based on the high-speed drive pulse trainSP10 in the high-speed drive mode, which are illustrated in FIG. 10(b),are not limited to those drive waveforms, and any drive waveform thatcan subject the two-coil stepper motor to the rotational drive by 360°per step may be employed.

[Description of Operation of Driver Circuit in Second Embodiment: FIG.11]

Next, with reference to the operation table for each of the transistorsof FIG. 11, description is given of how each of the drive waveforms forthe high-speed drive pulse train SP10 and the normal drive pulse SP00 iscreated based on the ON/OFF operation of each of the transistors of thedriver circuit 40 in the second embodiment.

As described above, the driver circuit 40 in the second embodiment isformed of the eight buffer circuits, namely, the eight transistors P1 toP8 and the eight transistors N1 to N8, which are complementarilyconnected to each other, and the drive waveforms O1 to O8 are outputfrom the respective buffer circuits (see FIG. 9).

First, with reference to the left part of the operation table of FIG.11, description is given of the ON/OFF operation of each of thetransistors in the high-speed drive mode. The stepper motor 41 driven inthe high-speed drive mode (minute-hour hand drive) is driven based onthe drive waveforms O1 to O4, and hence the transistors P1 to P4 and thetransistors N1 to N4 of the driver circuit 40 are operated in thehigh-speed drive mode, to thereby output the drive waveforms O1 to O4.

In this case, in FIG. 11, in the first drive pulse SP11 of thehigh-speed drive pulse train SP10, the drive waveform O3 has a voltageof less than 0 V, and the other drive waveforms O1, O2, and O4 have avoltage of 0 V (see FIG. 10(b)). Thus, control is performed so that thetransistor N3 is turned on and the transistor P3 is turned off, whilethe other transistors P1, P2, and P4 are turned on and the transistorsN1, N2, and N4 are turned off.

Further, in the second drive pulse SP12, the drive waveforms O2 and O4have a voltage of less than 0 V, and the other drive waveforms O1 and O3have a voltage of 0 V (see FIG. 10(b)). Thus, control is performed sothat the transistors N2 and N4 are turned on and the transistors P2 andP4 are turned off, while the other transistors P1 and P3 are turned onand the transistors N1 and N3 are turned off.

Further, in the third drive pulse SP13, the drive waveform O4 has avoltage of less than 0 V, and the other drive waveforms O1, O2, and O3have a voltage of 0 V (see FIG. 10(b)). Thus, control is performed sothat the transistor N4 is turned on and the transistor P4 is turned off,while the other transistors P1, P2, and P3 are turned on and thetransistors N1, N2, and N3 are turned off.

Further, in the normal drive mode described later, the stepper motor 41is not driven, and all the drive waveforms O1 to O4 have a voltage of 0V. Thus, control is performed so that all the transistors P1 to P4 areturned on and all the transistors N1 to N4 are turned off.

Next, with reference to the right part of the operation table of FIG.11, description is given of the ON/OFF operation of each of thetransistors in the normal drive mode. The stepper motor 42 driven in thenormal drive mode (second hand drive) is driven based on the drivewaveforms O5 to O8, and hence the transistors P5 to P8 and thetransistors N5 to N8 of the driver circuit 40 are operated in the normaldrive mode, to thereby output the drive waveforms O5 to O8.

In this case, in FIG. 11, in the first drive pulse SP01 in the firststep of the normal drive pulse SP00, the drive waveform O7 has a voltageof less than 0 V, and the other drive waveforms O5, O6, and O8 have avoltage of 0 V (see FIG. 10(c)). Thus, control is performed so that thetransistor N7 is turned on and the transistor P7 is turned off, whilethe other transistors P5, P6, and P8 are turned on and the transistorsN5, N6, and N8 are turned off.

Further, in the second drive pulse SP02 in the second step of the normaldrive pulse SP00, the drive waveform O8 has a voltage of less than 0 V,and the other drive waveforms O5, O6, and O7 have a voltage of 0 V (seeFIG. 10(c)). Thus, control is performed so that the transistor N8 isturned on and the transistor P8 is turned off, while the othertransistors P5, P6, and P7 are turned on and the transistors N5, N6, andN7 are turned off.

Further, in the high-speed drive mode described above, the stepper motor42 is not driven, and all the drive waveforms O5 to O8 have a voltage of0 V. Thus, control is performed so that all the transistors P5 to P8 areturned on and all the transistors N5 to N8 are turned off.

In the operation table of FIG. 11, a position at which the ON/OFFoperation of each of the transistors is switched due to each drive pulseis shown by being surrounded by an ellipse. For example, in thehigh-speed drive mode, in the first drive pulse SP11, the drive waveformO3 has a voltage of less than 0 V, and hence the transistor P3 isswitched from ON to OFF, while the transistor N3 is switched from OFF toON. Thus, OFF for the transistor P3 and ON for the transistor N3 aresurrounded by ellipses, to thereby indicate that the operations of thetransistors P3 and N3 are switched due to the first drive pulse SP11.

Further, the operation of the stepper motor 41 being rotated by 360° perstep due to the high-speed drive pulse train SP10 is the same as theoperation of the stepper motor 20 in the above-mentioned firstembodiment (see FIG. 7), while the operation of the stepper motor 42 dueto the normal drive pulse SP00 is the same as the operation of therelated-art stepper motor described above (see FIG. 4 and FIG. 5), andhence description thereof is omitted here.

As described above, the electronic watch according to the secondembodiment includes two stepper motors, namely, the stepper motor 41configured to perform the high-speed drive based on the rotation by 360°per step for the minute-hour hand drive and the stepper motor 42configured to perform normal drive based on the rotation by 180° perstep for the second hand drive. Further, the drive frequency (outputinterval between drive pulses) of the normal drive pulse SP00 fordriving the stepper motor 42 configured to move the second hand is setlower than the drive frequency of the high-speed drive pulse train SP10for driving the stepper motor 41 configured to drive the minute-hourhands. With this, it is possible to achieve hand movements different indrive frequency by two stepper motors.

In this case, the second hand is generally smaller in hand shape and islighter in weight than other hands, and hence impact resistance thereofis not considered so important. However, the second hand is usuallymoved every second, and hence the drive frequency is high, whichincreases the importance of low-power-consumption drive. In addition,the minute-hour hands are generally larger in hand shape and heavier inweight than the secondhand, and hence impact resistance thereof isconsidered important, but the drive frequency is low, which eliminatesthe importance of the low-power-consumption drive.

Therefore, it is possible to increase the gear speed reduction ratio ofthe minute hand (to 1/60) by arranging the stepper motor 41 to berotated by 360° per step for the minute-hour hand drive, and hence it ispossible to achieve an increase in torque of the minute-hour hands andimprove the impact resistance of the minute-hour hands, to thereby beable to satisfy performance required for the minute-hour hands. Further,by arranging the stepper motor 42 configured to perform the normal drivebased on the rotation by 180° per step for the second hand drive, thegear speed reduction ratio of the second hand is 1/30 in the same manneras in the related art, but it is possible to achieve a one-shot drivepulse per step (see FIG. 10(c)), which enables the low-power-consumptiondrive.

Further, in the second embodiment, the high-speed drive pulse train SP10and the normal drive pulse SP00 are generated by arranging thehigh-speed drive pulse generation circuit 34 to switch a timing toselect a specific drive pulse from one drive pulse train, and hence itsuffices that only one drive pulse generation circuit is provided, whichis advantageous in that the circuit scale of the electronic watch can bereduced.

Third Embodiment

[Description of Configuration of Electronic Watch According to ThirdEmbodiment: FIG. 12]

Next, a schematic configuration of an electronic watch according to thethird embodiment is described with reference to FIG. 12. Referencesymbol 50 denotes an analog indication-type electronic watch accordingto the third embodiment. The electronic watch 50 includes an oscillationcircuit 52 configured to output the predetermined reference signal P1through use of a quartz crystal unit (not shown), a control circuit 53configured to receive as input the reference signal P1 to output controlsignals CN4, CN5, and CN6, a high-speed drive pulse generation circuit54, a normal drive pulse generation circuit 55, a switching controlcircuit 56, a selector 57, a driver circuit 60, and the two-coil steppermotor 20 (hereinafter referred to as “stepper motor 20”).

The electronic watch 50 includes an indication part including hands, awheel train, a power source, and an operation member, but illustrationthereof is omitted because those components do not directly relate tothe present invention.

The high-speed drive pulse generation circuit 54 receives the controlsignal CN4 as input, and generates and outputs a high-speed drive pulsetrain SP20 for driving the stepper motor 20 at high speed. Thehigh-speed drive pulse train SP20 indicates an example of having a drivewaveform different from that of the high-speed drive pulse train SP10 ineach of the above-mentioned first and second embodiments, and istherefore denoted by a different reference symbol. The high-speed drivepulse train SP20 is also formed of three drive pulses in the same manneras the high-speed drive pulse train SP10, but is described later indetail.

The normal drive pulse generation circuit 55 receives the control signalCN5 as input, and generates and outputs the normal drive pulse SP00 forsubjecting the stepper motor 20 to the normal drive. The normal drivepulse SP00 in the third embodiment has the same drive waveform as thatof the normal drive pulse SP00 in the second embodiment, and istherefore denoted by the same reference symbol.

The switching control circuit 56 receives the control signal CN6 asinput, and outputs a switching signal P4 for switching between thehigh-speed drive pulse train SP20 and the normal drive pulse SP00depending on the drive mode.

The selector 57 receives two kinds of drive pulses, namely, thehigh-speed drive pulse train SP20 and the normal drive pulse SP00 asinput, and selects and outputs any one of those two kinds of drivepulses based on the switching signal P4.

The driver circuit 60 receives, as input, any one of the drive pulses,namely, the high-speed drive pulse train SP20 or the normal drive pulseSP00 from the selector 57, and supplies the drive waveforms O1 to O4based on the drive pulse to the coil A and the coil B of the steppermotor 20, to thereby drive the stepper motor 20. The circuitconfiguration of the driver circuit 60 is the same as that of the drivercircuit 10 in the above-mentioned first embodiment (see FIG. 3), andhence the description of the circuit configuration and the operation ofeach of the transistors is omitted.

The stepper motor 20 includes two coils, namely, the coil A and the coilB as a first coil and a second coil, respectively, and is the same asthe stepper motor 20 in the first embodiment described above (see FIG.2). Thus, the stepper motor 20 is denoted by the same reference symbol,and detailed description of the configuration is omitted.

[Description of Operation of Electronic Watch According to ThirdEmbodiment: FIG. 12]

Next, with reference to FIG. 12, description is given of a schematicoperation of the electronic watch according to the third embodiment. Asdescribed above, the electronic watch 50 includes one stepper motor 20and two drive pulse generation circuits, namely, the high-speed drivepulse generation circuit 54 and the normal drive pulse generationcircuit 55.

The electronic watch 50 has the normal drive mode of, for example,moving the hand every second and the high-speed drive mode of moving thehand at high speed for time correction or other such purpose. In thiscase, when the electronic watch 50 is in the high-speed drive mode, thecontrol circuit 53 outputs the control signal CN4 to activate thehigh-speed drive pulse generation circuit 54, and outputs the high-speeddrive pulse train SP20. Meanwhile, when the electronic watch 50 is inthe normal drive mode, the control circuit 53 outputs the control signalCN5 to activate the normal drive pulse generation circuit 55, andoutputs the normal drive pulse SP00.

Further, when the electronic watch 50 selects the high-speed drive mode,the control circuit 53 outputs the control signal CN6 to operate theswitching control circuit 56, and outputs and transmits the switchingsignal P4 in the high-speed drive mode to the selector 57. The selector57 receives the switching signal P4 as input, and selects the high-speeddrive pulse train SP20 to output the high-speed drive pulse train SP20to the driver circuit 60.

The driver circuit 60 operates an internal buffer circuit based on thehigh-speed drive pulse train SP20 formed of a plurality of drive pulses,and sequentially outputs the drive waveforms O1 to O4 corresponding tothe high-speed drive to subject the stepper motor 20 to the high-speedrotational drive in increments of 360° per step.

Further, when the electronic watch 50 selects the normal drive mode, thecontrol circuit 53 outputs the control signal CN6 to operate theswitching control circuit 56, and outputs and transmits the switchingsignal P4 in the normal drive mode to the selector 57. The selector 57receives the switching signal P4 as input, and selects the normal drivepulse SP00 to output the normal drive pulse SP00 to the driver circuit60.

The driver circuit 60 operates the internal buffer circuit based on thenormal drive pulse SP00, and outputs the drive waveforms O1 to O4corresponding to the normal drive to subject the stepper motor 20 to thenormal rotational drive (for example, moving the hand every second) inincrements of 180° per step.

[Description of Rotational Drive by 360° Per Two Steps of Related-ArtTwo-Coil Stepper Motor: FIGS. 13]

Next, an example of the related-art high-speed drive operation performedby the two-coil stepper motor is described with reference to FIG. 13 forthe sake of comparison prior to the description of a high-speed driveoperation for the stepper motor in the third embodiment. Theconfiguration diagram of the third embodiment illustrated in FIG. 12 isemployed for the two-coil stepper motor and the driver circuit.

FIG. 13(a) is an example of the drive waveform for rotationally drivingthe rotor by 360° per two steps at high speed by subjecting the steppermotor 20 to the related-art rotation by 180° per step continuously intwo steps. In FIG. 13(a), in a first drive pulse SP1-1 in the firststep, the drive waveform O3 has a voltage of less than 0 V, and theother drive waveforms O1, O2, and O4 have a voltage of 0 V. With this, adrive current flows into the coil B of the stepper motor 20 connected tothe drive waveforms O3 and O4 to excite the coil B.

Next, in a second drive pulse SP1-2 in the first step, the drivewaveforms O2 and O3 have a voltage of less than 0 V, and the drivewaveforms O1 and O4 have a voltage of 0 V. With this, a drive currentflows into both the coil A and the coil B of the stepper motor 20, andboth the coil A and the coil B are excited in the same direction.

Next, in a first drive pulse SP2-1 in the second step, the drivewaveform O4 has a voltage of less than 0 V, and the other drivewaveforms O1, O2, and O3 have a voltage of 0 V. With this, a drivecurrent flows into the coil B of the stepper motor 20 connected to thedrive waveforms O3 and O4, and the coil B is excited in a directionreverse to that of the first step.

Next, in a second drive pulse SP2-2 in the second step, the drivewaveforms O1 and O4 have a voltage of less than 0 V, and the drivewaveforms O2 and O3 have a voltage of 0 V. With this, a drive currentflows into both the coil A and the coil B of the stepper motor 20, andboth the coil A and the coil B are excited in the direction reverse tothat of the first step.

Next, with reference to FIG. 13(b) to FIG. 13(e), description is givenof the operation of the stepper motor configured to perform therelated-art rotational drive by 360° per two steps. The referencesymbols of the respective members of the stepper motor 20 are writtenonly in FIG. 13(b) and omitted in the other figures. FIG. 13(b) is anillustration of an operation performed when the first drive pulse SP1-1in the first step is supplied to the stepper motor 20. In this case,when the first drive pulse SP1-1 is supplied, a drive current (notshown) flows from the coil terminal O4 into the coil terminal O3 toexcite the coil B in the direction indicated by the arrow.

With this, the second magnetic-pole portion 22 b is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil A is inhibited from being excited. Thus,the first magnetic-pole portion 22 a has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the first magnetic-pole portion 22 a and thethird magnetic-pole portion 22 c attract each other, and the S-pole ofthe rotor 21 and the N-pole of the second magnetic-pole portion 22 battract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom the stationary position of 0° to reach the position of about 135°.

Next, in FIG. 13(c), when the second drive pulse SP1-2 in the first stepis supplied, a drive current flows from the coil terminal O1 into thecoil terminal O2 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO4 into the coil terminal O3 to excite the coil B in the directionindicated by the arrow.

With this, the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b are magnetized to the N-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the S-pole. As a result, theN-pole of the rotor 21 and the S-pole of the third magnetic-pole portion22 c attract each other, and the S-pole of the rotor 21 and the N-polesof both the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b attract each other. Thus, the rotor 21 isfurther rotated in the counterclockwise direction, the N-pole of therotor 21 is rotated to reach the position of 180°, and becomesstationary. That is, the rotor 21 is rotated by 180° in the first step.

Next, in FIG. 13(d), when the first drive pulse SP2-1 in the second stepis supplied next, a drive current flows from the coil terminal O3 intothe coil terminal O4 to excite the coil B in the direction indicated bythe arrow. With this, the second magnetic-pole portion 22 b ismagnetized to the S-pole, and the third magnetic-pole portion 22 c ismagnetized to the N-pole. In addition, the coil A is inhibited frombeing excited. Thus, the first magnetic-pole portion 22 a has the N-polein the same manner as the third magnetic-pole portion 22 c.

As a result, the N-pole of the rotor 21 and the S-pole of the secondmagnetic-pole portion 22 b attract each other, while the S-pole of therotor 21 and the N-poles of the first magnetic-pole portion 22 a and thethird magnetic-pole portion 22 c attract each other. Thus, the rotor 21is rotated in the counterclockwise direction, and the N-pole of therotor 2 l is rotated to the position of about 315°.

Next, in FIG. 13(e), when the second drive pulse SP2-2 in the secondstep is supplied, a drive current flows from the coil terminal O2 intothe coil terminal O1 to excite the coil A in the direction indicated bythe arrow. Further, similarly, a drive current flows from the coilterminal O3 into the coil terminal O4 to excite the coil B in thedirection indicated by the arrow.

With this, the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b are magnetized to the S-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the N-pole. As a result, theS-pole of the rotor 21 and the N-pole of the third magnetic-pole portion22 c attract each other, and the N-pole of the rotor 21 and the S-polesof both the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b attract each other. Thus, the rotor 21 isfurther rotated in the counterclockwise direction, the N-pole of therotor 21 is rotated to reach the position of 360° (0°), and becomesstationary. That is, the rotor 21 is rotated by 180° in the second step,and rotationally driven by 360° in two steps in total.

In this manner, when the related-art rotational drive by 180° per stepis repeatedly performed, the rotor 21 is rotated by 360° at relativelyhigh speed, but the drive is still performed in two steps, whichrequires a total of four drive pulses, namely, the first drive pulseSP1-1 and the first drive pulse SP1-2 in the first step and the firstdrive pulse SP1-1 and the second drive pulse SP2-2 in the second step.Thus, this drive cannot be considered as maximizing the high-speedrotational performance of the stepper motor. In addition, the drivercircuit supplies a total of four drive pulses to the stepper motor inthe rotational drive by 360°, which raises another problem that drivepower consumption is high.

[Description of High-Speed Drive in Third Embodiment: FIGS. 14]

Next, with reference to FIG. 14, description is given of the high-speedrotational drive in increments of 360° per step in the high-speed drivemode in the third embodiment. FIG. 14(a) is an example of the drivewaveform of the high-speed drive pulse train SP20 for rotationallydriving the stepper motor 20 in increments of 360° per step. In thiscase, the high-speed drive pulse train SP20 in the third embodiment isformed of three drive pulses, namely, a first drive pulse SP21, a seconddrive pulse SP22, and a third drive pulse SP23.

In FIG. 14(a), in the first drive pulse SP21, the drive waveform O3 hasa voltage of less than 0 V, and the other drive waveforms O1, O2, and O4have a voltage of 0 V. With this, a drive current flows into the coil Bof the stepper motor 20 connected to the drive waveforms O3 and O4 toexcite the coil B.

Next, in the second drive pulse SP22, the drive waveforms O2 and O4 hasa voltage of less than 0 V, and the drive waveforms O1 and O3 have avoltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20, and both the coil A and the coilB are excited in such directions as to face each other.

Next, in the third drive pulse SP23, the drive waveforms O1 and O4 has avoltage of less than 0 V, and the drive waveforms O2 and O3 have avoltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20, and both the coil A and the coilB are excited in the same direction.

Next, with reference to FIG. 14(b) to FIG. 14(e), description is givenof the high-speed drive of the stepper motor in the rotation by 360° perstep in the high-speed drive mode in the third embodiment. The referencesymbols of the respective members of the stepper motor 20 are writtenonly in FIG. 14(b) and omitted in the other figures. FIG. 14(b) is anillustration of a stationary state of the stepper motor 20 and a statein which the N-pole of the rotor 21 of the stepper motor 20 is locatedat the stationary position of 0° (upward direction on the figure) and isheld.

Next, FIG. 14(c) is an illustration of an operation performed when thefirst drive pulse SP21 is supplied after the stationary state of thestepper motor 20. In this case, when the first drive pulse SP21 issupplied, a drive current (not shown) flows from the coil terminal O4into the coil terminal O3 to excite the coil B in the directionindicated by the arrow.

With this, the second magnetic-pole portion 22 b is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil A is inhibited from being excited. Thus,the first magnetic-pole portion 22 a has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the first magnetic-pole portion 22 a and thethird magnetic-pole portion 22 c attract each other, and the S-pole ofthe rotor 21 and the N-pole of the second magnetic-pole portion 22 battract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom the stationary position of 0° to reach the position of about 135°.

Next, in FIG. 14(d), in a case where the subsequent second drive pulseSP22 is supplied when the N-pole of the rotor 21 is positioned nearabout 135°, a drive current flows from the coil terminal O1 into thecoil terminal O2 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO3 into the coil terminal O4 to excite the coil B in the directionindicated by the arrow.

With this, the first magnetic-pole portion 22 a is magnetized to theN-pole, the second magnetic-pole portion 22 b is magnetized to theS-pole, and the third magnetic-pole portion 22 c is not magnetized dueto canceled magnetization. As a result, the N-pole of the rotor 21 andthe S-pole of the second magnetic-pole portion 22 b attract each other,and the S-pole of the rotor 21 and the N-pole of the first magnetic-poleportion 22 a attract each other. Thus, the rotor 21 is further rotatedin the counterclockwise direction, and the N-pole of the rotor 21 isrotated to reach the position of about 270°.

Next, in FIG. 14(e), in a case where the subsequent third drive pulseSP23 is supplied when the N-pole of the rotor 21 is positioned nearabout 270°, a drive current flows from the coil terminal O2 into thecoil terminal O1 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO3 into the coil terminal O4 to excite the coil B in the directionindicated by the arrow.

With this, the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b are magnetized to the S-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the N-pole. As a result, theS-pole of the rotor 21 and the N-pole of the third magnetic-pole portion22 c attract each other, and the N-pole of the rotor 21 and the S-polesof both the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b attract each other. Thus, the rotor 21 isfurther rotated in the counterclockwise direction, and the N-pole of therotor 21 is rotated to reach the position of about 360° (0°). In thismanner, the stepper motor 20 can achieve the high-speed rotational drivein increments of 360° per step based on the high-speed drive pulse trainSP20 formed of three drive pulses.

In this case, as illustrated in FIG. 14(e), when the high-speed drivepulse train SP20 is continuously supplied at the time of the rotor 21returning to the position of 360° (0°), as illustrated in FIG. 14(c),the second magnetic-pole portion 22 b is again magnetized to the N-pole,and the third magnetic-pole portion 22 c and the first magnetic-poleportion 22 a are again magnetized to the S-pole, due to the first drivepulse SP21 at the head. As a result, the N-pole of the rotor 21 and theS-poles of the first magnetic-pole portion 22 a and the thirdmagnetic-pole portion 22 c attract each other, and the S-pole of therotor 21 and the N-pole of the second magnetic-pole portion 22 b attracteach other. Thus, the rotor 21 is continuously rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom the stationary position of 0° to reach the position of about 135°.

After that, the respective drive pulses of the high-speed drive pulsetrain SP20 are continuously supplied, to thereby cause the rotor 21 ofthe stepper motor 20 to repeat the rotational operation illustrated inFIG. 14(c) to FIG. 14(e). That is, the continuous output of thehigh-speed drive pulse train SP20 causes the stepper motor 20 tocontinue the high-speed rotational drive in increments of 360° per step.

The normal drive in the normal drive mode in the third embodiment is thesame as the related-art rotational drive by 180° per step, which isillustrated and shown in FIG. 4 and FIG. 5, and hence descriptionthereof is omitted here. Then, it is possible to move the second handevery second by outputting the normal drive pulse SP00 in the normaldrive mode at a cycle of, for example, one second.

As described above, according to the third embodiment, the rotationaldrive by 360° per step can be achieved by as few as three drive pulses,and hence compared with the related-art two-step drive (see FIG. 13), itis possible to perform the high-speed drive at a speed close to therotation limit of the stepper motor.

Further, it is possible to continuously rotate the stepper motor 20 athigh speed by continuously outputting the high-speed drive pulse trainSP20. With this, for example, in the fast-forwarding operation of thehands, the fast-forwarding operation can be performed at a speed higherthan in the related art, which enables the time correction or the likeof the hands to be performed quickly in a short period of time.

Further, although four drive pulses are required for the related-arttwo-step drive (see FIG. 13), in the third embodiment, the rotationaldrive by 360° per step can be achieved by as few as three drive pulses,and hence it is possible to achieve the low-power-consumption drive byan amount corresponding to the reduced number of drive pulses.

Further, the drive pulse is required to be provided with a sufficientdrive force in consideration of, for example, individual differences ofthe stepper motor 20 or power supply variation, and hence the rotor 21of the stepper motor 20 is often rotated with an overlap of anelectromagnetic stable point for each drive pulse. When this overlap ispresent, there is a case in which the rotor 21 is rotated slightlybackward or vibrated minutely. Such movement of the rotor 21 is a lossfor the stepper motor 20, and causes a reduction in driving efficiency.However, in the third embodiment, the rotational drive by 360° isachieved by as few as three drive pulses of the high-speed drive pulsetrain SP20, and hence the number of times of overlapping of the rotor 21is reduced, with the result that the driving efficiency of the steppermotor is improved.

In this manner, in the third embodiment, in the high-speed drive mode,the high-speed drive pulse train SP20 is continuously output, to therebydrive the rotor of the stepper motor with a drive frequency higher thanthat of the normal drive pulse SP00 in the normal drive mode (forexample, moving the hand every second), which enables the hands to bedriven at high speed.

In the third embodiment, there are provided two drive pulse generationcircuits, namely, the high-speed drive pulse generation circuit 54 andthe normal drive pulse generation circuit 55, but the present inventionis not limited to this configuration, and as in the second embodiment,the high-speed drive pulse train and a normal drive pulse from one drivepulse generation circuit may be selected and switched depending on thetiming.

[Description of High-Speed Drive in Modification Example 1 of ThirdEmbodiment: FIGS. 15]

Next, with reference to FIG. 15, description is given of the high-speeddrive of the two-coil stepper motor in Modification Example 1 of thethird embodiment. Respective modification examples including othermodification examples described later are different only in drivewaveform of the high-speed drive pulse train. Thus, description is givenof only the drive waveform in the high-speed drive mode and a high-speeddrive operation for the stepper motor, and the configuration diagram ofeach modification example and the description of the normal drive modeare omitted.

FIG. 15(a) is an example of the drive waveform of a high-speed drivepulse train SP30 for performing the rotational drive by 360° per step inModification Example 1 of the third embodiment. In FIG. 15(a), thehigh-speed drive pulse train SP30 is formed of three drive pulses,namely, a first drive pulse SP31, a second drive pulse SP32, and a thirddrive pulse SP33.

In the first drive pulse SP31, the drive waveform O3 has a voltage ofless than 0 V, and the other drive waveforms O1, O2, and O4 have avoltage of 0 V. With this, a drive current flows into the coil B of thestepper motor 20 connected to the drive waveforms O3 and O4 to excitethe coil B.

Next, in the second drive pulse SP32, the drive waveform O2 has avoltage of less than 0 V, and the other drive waveforms O1, O2, and O4have a voltage of 0 V. With this, a drive current flows into the coil Aof the stepper motor 20 connected to the drive waveforms O1 and O2 toexcite the coil A.

Next, in the third drive pulse SP33, the drive waveforms O1 and O4 has avoltage of less than 0 V, and the drive waveforms O2 and O3 have avoltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20, and both the coil A and the coilB are excited in the same direction.

Next, with reference to FIG. 15(b) to FIG. 15(e), description is givenof the high-speed drive of the stepper motor in the rotation by 360° perstep in Modification Example 1. The reference symbols of the respectivemembers of the stepper motor 20 are written only in FIG. 15(b) andomitted in the other figures. FIG. 15(b) is an illustration of astationary state of the stepper motor 20 and a state in which the N-poleof the rotor 21 of the stepper motor 20 is located at the stationaryposition of 0° (upward direction on the figure) and is held.

Next, FIG. 15(c) is an illustration of an operation performed when thefirst drive pulse SP31 is supplied after the stationary state of thestepper motor 20. In this case, when the first drive pulse SP31 issupplied, a drive current (not shown) flows from the coil terminal O4into the coil terminal O3 to excite the coil B in the directionindicated by the arrow.

With this, the second magnetic-pole portion 22 b is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil A is inhibited from being excited. Thus,the first magnetic-pole portion 22 a has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the first magnetic-pole portion 22 a and thethird magnetic-pole portion 22 c attract each other, and the S-pole ofthe rotor 21 and the N-pole of the second magnetic-pole portion 22 battract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom the stationary position of 0° to reach the position of about 135°.

Next, in FIG. 15(d), in a case where the subsequent second drive pulseSP32 is supplied when the N-pole of the rotor 21 is positioned nearabout 135°, a drive current flows from the coil terminal O1 into thecoil terminal O2 to excite the coil A in the direction indicated by thearrow.

With this, the first magnetic-pole portion 22 a is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil B is inhibited from being excited. Thus,the second magnetic-pole portion 22 b has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the second magnetic-pole portion 22 b andthe third magnetic-pole portion 22 c attract each other, and the S-poleof the rotor 21 and the N-pole of the first magnetic-pole portion 22 aattract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotated toreach the position of about 225°.

Next, in FIG. 15(e), in a case where the subsequent third drive pulseSP33 is supplied when the N-pole of the rotor 21 is positioned nearabout 225°, a drive current flows from the coil terminal O2 into thecoil terminal O1 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO3 into the coil terminal O4 to excite the coil B in the same directionas that of the coil A.

With this, the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b are magnetized to the S-pole, and the thirdmagnetic-pole portion 22 c is magnetized to the N-pole. As a result, theS-pole of the rotor 21 and the N-pole of the third magnetic-pole portion22 c attract each other, and the N-pole of the rotor 21 and the S-polesof both the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b attract each other. Thus, the rotor 21 isfurther rotated in the counterclockwise direction, and the N-pole of therotor 21 is rotated to reach the position of about 360° (0°). In thismanner, also in Modification Example 1, the stepper motor 20 can achievethe high-speed rotational drive in increments of 360° per step based onthe high-speed drive pulse train SP30 formed of three drive pulses.

As described above, according to Modification Example 1 of the thirdembodiment, the rotational drive by 360° per step can be achieved by asfew as three drive pulses, and hence it is possible to obtain the sameexcellent effects as those of the third embodiment.

[Description of High-Speed Drive in Modification Example 2 of ThirdEmbodiment: FIGS. 16]

Next, with reference to FIG. 16, description is given of the high-speeddrive of the two-coil stepper motor in Modification Example 2 of thethird embodiment. FIG. 16(a) is an example of the drive waveform of ahigh-speed drive pulse train SP40 for performing the rotational drive by360° per step in Modification Example 2 of the third embodiment.

In FIG. 16(a), the high-speed drive pulse train SP40 is formed of threedrive pulses, namely, a first drive pulse SP41, a second drive pulseSP42, and a third drive pulse SP43. In the first drive pulse SP41, thedrive waveform O3 has a voltage of less than 0 V, and the other drivewaveforms O1, O2, and O4 have a voltage of 0 V. With this, a drivecurrent flows into the coil B of the stepper motor 20 connected to thedrive waveforms O3 and O4 to excite the coil B.

Next, in the second drive pulse SP42, the drive waveforms O2 and O4 havea voltage of less than 0 V, and the drive waveforms O1 and O3 have avoltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20 to excite the coil A and the coilB in directions opposed to each other.

Next, in the third drive pulse SP43, the drive waveform O1 has a voltageof less than 0 V, and the drive waveforms O2, O3, and O4 have a voltageof 0 V. With this, a drive current flows into the coil A of the steppermotor 20 to excite the coil A.

Next, with reference to FIG. 16(b) to FIG. 16(e), description is givenof the high-speed drive of the stepper motor in the rotation by 360° perstep in Modification Example 2. The reference symbols of the respectivemembers of the stepper motor 20 are written only in FIG. 16(b) andomitted in the other figures. FIG. 16(b) is an illustration of astationary state of the stepper motor 20 and a state in which the N-poleof the rotor 21 of the stepper motor 20 is located at the stationaryposition of 0° (upward direction on the figure) and is held.

Next, FIG. 16(c) is an illustration of an operation performed when thefirst drive pulse SP41 is supplied after the stationary state of thestepper motor 20. In this case, when the first drive pulse SP41 issupplied, a drive current flows from the coil terminal O4 into the coilterminal O3 to excite the coil B in the direction indicated by thearrow.

With this, the second magnetic-pole portion 22 b is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil A is inhibited from being excited. Thus,the first magnetic-pole portion 22 a has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the first magnetic-pole portion 22 a and thethird magnetic-pole portion 22 c attract each other, and the S-pole ofthe rotor 21 and the N-pole of the second magnetic-pole portion 22 battract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotatedfrom the stationary position of 0° to reach the position of about 135°.

Next, in FIG. 16(d), in a case where the subsequent second drive pulseSP42 is supplied when the N-pole of the rotor 21 is positioned nearabout 135°, a drive current flows from the coil terminal O1 into thecoil terminal O2 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO3 into the coil terminal O4 to excite the coil B in the directionindicated by the arrow.

With this, the first magnetic-pole portion 22 a is magnetized to theN-pole, the second magnetic-pole portion 22 b is magnetized to theS-pole, and the third magnetic-pole portion 22 c is not magnetized dueto canceled magnetization. As a result, the N-pole of the rotor 21 andthe S-pole of the second magnetic-pole portion 22 b attract each other,and the S-pole of the rotor 21 and the N-pole of the first magnetic-poleportion 22 a attract each other. Thus, the rotor 21 is further rotatedin the counterclockwise direction, and the N-pole of the rotor 21 isrotated to reach the position of about 270°.

Next, in FIG. 16(e), in a case where the subsequent third drive pulseSP43 is supplied when the N-pole of the rotor 21 is positioned nearabout 270°, a drive current flows from the coil terminal O2 into thecoil terminal O1 to excite the coil A in the direction indicated by thearrow.

With this, the first magnetic-pole portion 22 a is magnetized to theS-pole, and the third magnetic-pole portion 22 c is magnetized to theN-pole. In addition, the coil B is inhibited from being excited. Thus,the second magnetic-pole portion 22 b has the N-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-pole of the first magnetic-pole portion 22 a attracteach other, and the S-pole of the rotor 21 and the N-poles of the secondmagnetic-pole portion 22 b and the third magnetic-pole portion 22 cattract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotated toreach the position exceeding about 360° (0°) as illustrated in FIG.16(e). After that, when the third drive pulse SP43 is ended, the N-poleof the rotor 21 returns to the position of the stationary position of360° (0°), and becomes stationary.

When the high-speed drive pulse train SP40 is continuously output, theN-pole of the rotor 21 avoids returning from the position exceedingabout 360° (0°), and the N-pole of the rotor 21 is rotated to reach theposition of about 135° due to the subsequent first drive pulse SP41 (seeFIG. 16(c)). After that, the high-speed rotational drive is continued.In this manner, also in Modification Example 2, the stepper motor 20 canachieve the high-speed rotational drive in increments of 360° per stepbased on the high-speed drive pulse train SP40 formed of three drivepulses.

As described above, according to Modification Example 2 of the thirdembodiment, the rotational drive by 360° per step can be achieved by asfew as three drive pulses, and hence it is possible to obtain the sameexcellent effects as those of the third embodiment.

[Description of High-Speed Drive in Modification Example 3 of ThirdEmbodiment: FIGS. 17]

Next, with reference to FIG. 17, description is given of the high-speeddrive of the two-coil stepper motor in Modification Example 3 of thethird embodiment. FIG. 17(a) is an example of the drive waveform of thehigh-speed drive pulse train SP50 for performing the rotational drive by360° per step in Modification Example 3 of the third embodiment.

In FIG. 17(a), the high-speed drive pulse train SP50 is formed of threedrive pulses, namely, a first drive pulse SP51, a second drive pulseSP52, and a third drive pulse SP53. In the first drive pulse SP51, thedrive waveforms O1 and O3 have a voltage of less than 0 V, and the drivewaveforms O2 and O4 have a voltage of 0 V. With this, a drive currentflows into both the coil A and the coil B of the stepper motor 20 toexcite the coil A and the coil B.

Next, in the second drive pulse SP52, the drive waveform O2 has avoltage of less than 0 V, and the drive waveforms O1, O3, and O4 have avoltage of 0 V. With this, a drive current flows into the coil A of thestepper motor 20 to excite the coil A.

Next, in the third drive pulse SP53, the drive waveforms O1 and O4 havea voltage of less than 0 V, and the drive waveforms O2 and O3 have avoltage of 0 V. With this, a drive current flows into both the coil Aand the coil B of the stepper motor 20 to excite both the coil A and thecoil B in the same direction.

Next, with reference to FIG. 17(b) to FIG. 17(e), description is givenof the high-speed drive of the stepper motor configured to perform therotation by 360° per step in Modification Example 3. The referencesymbols of the respective members of the stepper motor 20 are writtenonly in FIG. 17(b) and omitted in the other figures. FIG. 17(b) is anillustration of the stationary state of the stepper motor 20 and a statein which the N-pole of the rotor 21 of the stepper motor 20 is locatedat the stationary position of 0° (upward direction on the figure) and isheld.

Next, FIG. 17(c) is an illustration of an operation performed when thefirst drive pulse SP51 is supplied after the stationary state of thestepper motor 20. In this case, when the first drive pulse SP51 issupplied, a drive current flows from the coil terminal O2 into the coilterminal O1 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO4 into the coil terminal O3 to excite the coil B in the directionindicated by the arrow.

With this, the first magnetic-pole portion 22 a is magnetized to theS-pole, the second magnetic-pole portion 22 b is magnetized to theN-pole, and the third magnetic-pole portion 22 c is not magnetized dueto canceled magnetization. As a result, the N-pole of the rotor 21 andthe S-pole of the first magnetic-pole portion 22 a attract each other,and the S-pole of the rotor 21 and the N-pole of the secondmagnetic-pole portion 22 b attract each other. Thus, the rotor 21 isrotated in the counterclockwise direction, and the N-pole of the rotor21 is rotated from the stationary position of 0° to reach the positionof about 90°.

Next, in FIG. 17(d), in a case where the subsequent second drive pulseSP52 is supplied when the N-pole of the rotor 21 is positioned nearabout 90°, a drive current flows from the coil terminal O1 into the coilterminal O2 to excite the coil A in the direction indicated by thearrow.

With this, the first magnetic-pole portion 22 a is magnetized to theN-pole, and the third magnetic-pole portion 22 c is magnetized to theS-pole. In addition, the coil B is inhibited from being excited. Thus,the second magnetic-pole portion 22 b has the S-pole in the same manneras the third magnetic-pole portion 22 c. As a result, the N-pole of therotor 21 and the S-poles of the second magnetic-pole portion 22 b andthe third magnetic-pole portion 22 c attract each other, and the S-poleof the rotor 21 and the N-pole of the first magnetic-pole portion 22 aattract each other. Thus, the rotor 21 is further rotated in thecounterclockwise direction, and the N-pole of the rotor 21 is rotated toreach the position of about 225°.

Next, in FIG. 17(e), in a case where the subsequent third drive pulseSP53 is supplied when the N-pole of the rotor 21 is positioned nearabout 225°, a drive current flows from the coil terminal O2 into thecoil terminal O1 to excite the coil A in the direction indicated by thearrow. Further, similarly, a drive current flows from the coil terminalO3 into the coil terminal O4 to excite the coil B in the same directionas that of the coil A.

With this, the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b are both magnetized to the S-pole, and thethird magnetic-pole portion 22 c is magnetized to the N-pole. As aresult, the S-pole of the rotor 21 and the N-pole of the thirdmagnetic-pole portion 22 c attract each other, and the N-pole of therotor 21 and the S-poles of the first magnetic-pole portion 22 a and thesecond magnetic-pole portion 22 b attract each other. Thus, the rotor 21is further rotated in the counterclockwise direction, and the N-pole ofthe rotor 21 is rotated to reach the position of 360° (0°). In thismanner, also in Modification Example 3, the stepper motor 20 can achievethe high-speed rotational drive in increments of 360° per step based onthe high-speed drive pulse train SP50 formed of three drive pulses.

As described above, according to Modification Example 3 of the thirdembodiment, the rotational drive by 360° per step can be achieved by asfew as three drive pulses, and hence it is possible to obtain the sameexcellent effects as those of the third embodiment.

Fourth Embodiment

[Description of Configuration of Electronic Watch According to FourthEmbodiment: FIG. 18]

Next, a schematic configuration of an electronic watch according to afourth embodiment of the present invention is described with referenceto FIG. 18. Reference symbol 70 denotes an analog indication-typeelectronic watch according to the fourth embodiment. The electronicwatch 70 is similar to that of the first embodiment described above inthat the electronic watch 70 includes, as basic components, anoscillation circuit 72 configured to output the predetermined referencesignal P1, a control circuit 73 configured to receive as input thereference signal P1 to output the control signal CN1, a high-speed drivepulse generation circuit 74, a driver circuit 80, and the stepper motor20.

In the fourth embodiment, two coils, namely, the coil A and the coil B,of the stepper motor 20 and the driver circuit 80 are connected to eachother so as to short-circuit the coil terminals corresponding to thecoil terminal O2 and the coil terminal O4 described in the firstembodiment with reference to FIG. 1. Therefore, three drive waveforms,namely, the drive waveform O1, a drive waveform O2′, and the drivewaveform O3 are supplied from the driver circuit 80. The drive waveformO1 is supplied to the coil terminal O1 of the coil A, and the drivewaveform O3 is supplied to the coil terminal O3 of the coil B, while thedrive waveform O2′ is supplied to the coil terminals O2′ of the coil Aand the coil B in common.

The high-speed drive pulse generation circuit 74 receives the controlsignal CN1 as input, and generates and outputs a high-speed drive pulsetrain SP60 for driving the stepper motor 20 at high speed. Thehigh-speed drive pulse train SP60 indicates an example of having a drivewaveform different from that of the high-speed drive pulse trains SP10and SP20 in each of the above-mentioned embodiments, and is thereforedenoted by a different reference symbol. The high-speed drive pulsetrain SP60 is also formed of three drive pulses.

[Description of Circuit Configuration of Driver Circuit: FIG. 19]

Next, with reference to FIG. 19, description is given of an example ofthe circuit configuration of the driver circuit 80 configured to drivethe stepper motor 20. The driver circuit 80 is formed of three buffercircuits configured to supply three drive waveforms to the coil A andthe coil B of the stepper motor 20.

A buffer circuit including the transistor P1 being a P-channel MOStransistor and the transistor N1 being an N-channel MOS transistor,which are complementarily connected to each other, is connected to thecoil terminal O1 of the coil A, and outputs the drive waveform O1.

A buffer circuit including the transistor P3 being a P-channel MOStransistor and the transistor N3 being an N-channel MOS transistor,which are complementarily connected to each other, is connected to thecoil terminal O3 of the coil B, and outputs the drive waveform O3.

In addition, a buffer circuit including a transistor P2′ being aP-channel MOS transistor and a transistor N2′ being an N-channel MOStransistor, which are complementarily connected to each other, isconnected to the coil terminals O2′ provided to the coil A and the coilB in common, and is configured to output the drive waveform O2′ to thecoil A and the coil B in common.

[Description of Generation of Drive Pulse and Drive Waveform in FourthEmbodiment: FIGS. 20]

Next, with reference to FIG. 20, description is given of an example ofthe drive waveform of a high-speed drive pulse for rotationally drivingthe stepper motor in the fourth embodiment in increments of 360° perstep and the operation of each of the transistors of the driver circuit.

First, the high-speed drive pulse train SP60 is used for rotationallydriving the rotor of the stepper motor 20 of FIG. 18 from the stationaryposition of 0° in the forward rotation direction (counterclockwise) inincrements of 360°. FIG. 20(a) is an illustration of a drive waveformbased on the high-speed drive pulse SP60 and the three drive waveformsO1, O2′, and O3 to be output from the driver circuit 80.

In FIG. 20(a), the high-speed drive pulse train SP60 to be output fromthe high-speed drive pulse generation circuit 74 is, in this example, apulse train composed of 3 bits, namely, SP61 to SP63 and formed of thethree drive pulses, namely, the first drive pulse SP61, the second drivepulse SP62, and the third drive pulse SP63 in time series, whichincludes a logical “1” or a logical “0” in order to turn on/off each ofthe transistors of the driver circuit 80.

In the first drive pulse SP1, the drive waveform O3 has a voltage ofless than 0 V, and the other drive waveforms O1 and O2′ have a voltageof 0 V. With this, a drive current flows into the coil B of the steppermotor 20 connected to the coil terminals O2′ and O3 to excite the coilB.

Further, in the second drive pulse SP62, the drive waveform O2′ has avoltage of less than 0 V, and the drive waveforms O1 and O3 have avoltage of 0 V. Then, the drive waveform O2′ is applied to both the coilA and the coil B, which causes a drive current to flow into the coil Aand the coil B of the stepper motor 20 to excite both the coil A and thecoil B.

Further, in the third drive pulse SP63, the drive waveforms O1 and O2′have a voltage of less than 0 V, and the other drive waveform O3 has avoltage of 0 V. With this, a drive current flows into the coil B of thestepper motor 20 connected to the drive waveforms O2′ and O3 to excitethe coil B in a direction reverse to that of the first drive pulse SP61.

Next, with reference to the operation table of FIG. 20(b), descriptionis given of the operation of each of the transistors of the drivercircuit 80 based on the high-speed drive pulse train SP60. In regard tothe driver circuit, FIG. 19 is referred to. In FIG. 20(b), in the firstdrive pulse SP61, the drive waveform O3 has a voltage of less than 0 V,and the other drive waveforms O1 and O2′ have a voltage of 0 V. Thus,the transistors P2′ and N3 are turned on, while the transistors N2′ andP3 are turned off, and a drive current flows from the coil terminal O2′of the coil B into the coil terminal O3 to excite the coil B.

Further, the transistor N1 is turned off, the transistor P1 is turnedon, and both the drive waveforms O1 and O2′ have a voltage of 0 V. Thus,a drive current is not caused to flow into the coil A, which inhibitsthe coil A from being excited. In this case, the transistor P1 is turnedon, but may be turned off. In FIG. 20(b), this is written as “OFF” inparentheses.

Further, in the second drive pulse SP62, the drive waveform O2′ has avoltage of less than 0 V, and the other drive waveforms O1 and O3 have avoltage of 0 V. Thus, the transistors P1, N2′, and P3 are turned on, andthe transistors N1, P2′, and N3 are turned off. Then, a drive currentflows from the coil terminal O1 of the coil A into the coil terminal O2′while flowing from the coil terminal O3 of the coil B into the coilterminal O2′, and hence the coil A and the coil B are both excited.

Further, in the third drive pulse SP63, the drive waveform O1 has avoltage of less than 0 V, and the other drive waveforms O2′ and O3 havea voltage of 0 V. Thus, the transistors N2′ and P3 are turned on, whilethe transistors P2′ and N3 are turned off, and a drive current flowsfrom the coil terminal O3 of the coil B into the coil terminal O2′ toexcite the coil B.

Further, the transistor P1 is turned off, the transistor N1 is turnedon, and both the drive waveforms O1 and O2′ have a voltage of less than0 V. Thus, a drive current is not caused to flow into the coil A, whichinhibits the coil A from being excited. In this case, the transistor N1is turned on, but may be turned off.

In this manner, each of the transistors of the driver circuit 80 isON/OFF controlled based on the three drive pulses, namely, the first tothird drive pulses SP61 to SP63 of the high-speed drive pulse trainSP60, to thereby excite the coils A and B of the stepper motor 20.

[Description of Rotational Drive by 360° Per Step in Fourth Embodiment:FIGS. 7]

The high-speed rotational drive of the stepper motor 20 in increments of360° per step in the fourth embodiment is the same as that in the firstembodiment, and is therefore described with reference to FIG. 7. First,FIG. 7(a) is an illustration of a state in which the first drive pulseSP61 of the high-speed drive pulse train SP60 is supplied to the steppermotor 20. The coil B is excited in the direction indicated by the arrow,and hence the second magnetic-pole portion 22 b is magnetized to theN-pole, while the third magnetic-pole portion 22 c is magnetized to theS-pole. Meanwhile, the coil A is not magnetized, and hence the firstmagnetic-pole portion 22 a has the S-pole in the same manner as thethird magnetic-pole portion 22 c. Therefore, the rotor 21 is rotated inthe counterclockwise direction, and the N-pole of the rotor 21 isrotated in the counterclockwise direction from the stationary positionof 0° to reach the position of about 135°.

Next, as illustrated in FIG. 7(b), when the second drive pulse SP62 issupplied, both the coil A and the coil B are excited in the directionindicated by the arrow. Thus, the first magnetic-pole portion 22 a ismagnetized to the N-pole, the second magnetic-pole portion 22 b ismagnetized to the S-pole, and the third magnetic-pole portion 22 c isnot magnetized. As a result, the rotor 21 is further rotated in thecounterclockwise direction, the N-pole of the rotor 21 is rotated toreach the position of about 270°.

Further, as illustrated in FIG. 7(c), when the third drive pulse SP63 issupplied, the coil B is excited in the direction indicated by the arrow.Thus, the second magnetic-pole portion 22 b is magnetized to the S-pole,and the third magnetic-pole portion 22 c is magnetized to the N-pole. Inaddition, the coil A is inhibited from being excited. Thus, the firstmagnetic-pole portion 22 a has the N-pole in the same manner as thethird magnetic-pole portion 22 c. As a result, the rotor 21 is furtherrotated in the counterclockwise direction without stopping, and theN-pole of the rotor 21 is rotated to reach the position of about 315°.

After that, as illustrated in FIG. 7(d), when the supply of thehigh-speed drive pulse train SP60 is ended, the drive waveforms O1, O2′,and O3 all have a voltage of 0 V, and the coil A and the coil B stopbeing excited, which cancels the magnetization of the first to thirdmagnetic-pole portions, and the rotor 21 continues to rotate untilreaching the statically stable point of 360° (0°) without stopping, andis held at that position. In this manner, the stepper motor 20 isrotationally driven by 360° through one-step drive based on thehigh-speed drive pulse train SP60 formed of the three drive pulses SP61to SP63.

In this manner, with the electronic watch according to the fourthembodiment, even when the coil terminals O2′ of the coil A and the coilB are short-circuited to be used in common, it is possible to performthe rotational drive by 360° in one step by supplying the high-speeddrive pulse train SP60 formed of the three drive pulses SP61 to 63. Inthis case, it suffices that the number of drive waveforms to be suppliedis three and that the number of transistors is smaller than that in thefirst embodiment, which is effective in miniaturization of the circuitscale and reduction in cost.

It is to be understood that, by setting the gear speed reduction ratioto 1/60, it is possible to obtain the effect of an increase in torque ofthe hands and the effect of improvement in impact resistance, as well asthe effect that the movement of the hands becomes smoother to achievesatisfactory appearance, in the same manner as those of the firstembodiment.

It is also to be understood that the rotational drive by 360° throughone-step drive in the fourth embodiment may replace the rotational driveby 360° per step in the high-speed drive mode in the second embodiment.

Fifth Embodiment

[Description of Configuration of Electronic Watch According to FifthEmbodiment and Circuit Configuration of Driver Circuit in FifthEmbodiment: FIG. 18 and FIG. 19]

Next, description is given of an electronic watch according to a fifthembodiment of the present invention. A schematic configuration of theelectronic watch 70 according to the fifth embodiment is the same asthat of the fourth embodiment described above as illustrated in FIG. 18.The same applies to basic components included in the electronic watch70, namely, the oscillation circuit 72 configured to output thereference signal P1, the control circuit 73 configured to receive asinput the reference signal P1 to output the control signal CN1, thehigh-speed drive pulse generation circuit 74, the driver circuit 80, andthe stepper motor 20. However, there is a difference in high-speed drivepulse output from the high-speed drive pulse generation circuit 74, andhence reference symbol SP60 in FIG. 18 is replaced here by referencesymbol SP70 in the fifth embodiment.

In addition, the circuit configuration of the driver circuit 80configured to drive the stepper motor 20 in the fifth embodiment is alsothe same as that in the fourth embodiment described above, and henceFIG. 19 is referred to here.

[Description of Generation of Drive Pulse and Drive Waveform in FifthEmbodiment: FIGS. 21]

Next, with reference to FIG. 21, description is given of an example ofthe drive waveform of a high-speed drive pulse for rotationally drivingthe stepper motor in the fifth embodiment in increments of 360° per stepand the operation of each of the transistors of the driver circuit.

First, the high-speed drive pulse train SP70 is used for rotationallydriving the rotor of the stepper motor 20 of FIG. 18 from the stationaryposition of 0° in the forward rotation direction (counterclockwise) inincrements of 360°. FIG. 21(a) is an illustration of a drive waveformbased on the high-speed drive pulse SP60 and the three drive waveformsO1, O2′, and O3 to be output from the driver circuit 80.

In FIG. 21(a), the high-speed drive pulse train SP70 to be output fromthe high-speed drive pulse generation circuit 74 is, in this example, apulse train composed of 3 bits, namely, SP71 to SP73 and formed of thethree drive pulses, namely, the first drive pulse SP71, the second drivepulse SP72, and the third drive pulse SP73 in time series, whichincludes a logical “1” or a logical “0” in order to turn on/off each ofthe transistors of the driver circuit 80.

In the first drive pulse SP1, the drive waveform O3 has a voltage ofless than 0 V, and the other drive waveforms O1 and O2′ have a voltageof 0 V. With this, a drive current flows into the coil B of the steppermotor 20 connected to the drive waveforms O2′ and O3 to excite the coilB.

Further, in the second drive pulse SP72, the drive waveform O2′ has avoltage of less than 0 V, and the drive waveforms O1 and O3 have avoltage of 0 V. Then, the drive waveform O2′ is applied to both the coilA and the coil B, which causes a drive current to flow into the coil Aand the coil B of the stepper motor 20 to excite both the coil A and thecoil B.

The third drive pulse SP73 includes a drive pulse SP73 a, in which thedrive waveform O1 has a voltage of less than 0 V and the drive waveformO2′ has a voltage of 0 V, and a drive pulse SP73 b, in which the drivewaveform O1 and the drive waveform O2′ both have a voltage of less than0 V. The drive pulse SP73 a and the drive pulse 73 b are repeated in aregular pattern to collectively form the drive pulse SP73. The otherdrive waveform O3 has a voltage of 0 V. With this, while the drive pulseSP73 a is applied, a drive current flows into the coil A of the steppermotor 20 connected to the coil terminals O2′ and O1 to excite the coilA, and while the drive pulse SP73 b is applied, a drive current flowsinto the coil B of the stepper motor 20 connected to the coil terminalsO2′ and O3 to excite the coil B.

Next, with reference to the operation table of FIG. 21(b), descriptionis given of the operation of each of the transistors of the drivercircuit 80 based on the high-speed drive pulse train SP70. In FIG.21(b), in the first drive pulse SP71, the drive waveform O3 has avoltage of less than 0 V, and the other drive waveforms O1 and O2′ havea voltage of 0 V. Thus, the transistors P2′ and N3 are turned on, whilethe transistors N2′ and P3 are turned off, and a drive current flowsfrom the coil terminal O2′ of the coil B into the coil terminal O3 toexcite the coil B.

Further, the transistor N1 is turned off, the transistor P1 is turnedon, and both the drive waveforms O1 and O2′ have a voltage of 0 V. Thus,a drive current is not caused to flow into the coil A, which inhibitsthe coil A from being excited. In this case, the transistor P1 is turnedon, but may be turned off.

Further, in the second drive pulse SP72, the drive waveform O2′ has avoltage of less than 0 V, and the other drive waveforms O1 and O3 have avoltage of 0 V. Thus, the transistors P1, N2′, and P3 are turned on, andthe transistors N1, P2′, and N3 are turned off. Then, a drive currentflows from the coil terminal O1 of the coil A into the coil terminal O2′while flowing from the coil terminal O3 of the coil B into the coilterminal O2′, and hence the coil A and the coil B are both excited.

Further, in the third drive pulse SP73, the drive waveform O1 and thedrive waveform O3 are maintained at a voltage of less than 0 V and avoltage of 0 V, respectively, and the voltage of the drive waveform O2′differs depending on the segment. In the segment of the third drivepulse SP73 a, the drive waveform O2′ has a voltage of 0 V, and hence thetransistor P2′ is turned on, while the transistor N2′ is turned off.Then, the transistors P1 and N3 are in an off state, and the transistorsN1 and P3 are in an on state. Thus, a drive current flows from the coilterminal O1 of the coil A into the coil terminal O2′ to excite the coilA. Meanwhile, in the segment of the third drive pulse SP73 b, the drivewaveform O2′ has a voltage of less than 0 V, and hence the transistorP2′ is turned off, while the transistor N2′ is turned on. Then,similarly, the transistors P1 and N3 are in an off state, and thetransistors N1 and P3 are in an on state. Thus, a drive current flowsfrom the coil terminal O2′ of the coil B into the coil terminal O3 toexcite the coil B.

In the segment of the third drive pulse SP73 a, the coil terminals O3and O2′ both have a voltage of 0 V. Thus, a drive current is not causedto flow into the coil B, which inhibits the coil B from being excited.At this time, the transistor P3 is turned on, but may be turned off.

Further, in the segment of the third drive pulse SP73 b, the coilterminals O1 and O2′ both have a voltage of −V. Thus, a drive current isnot caused to flow into the coil A, which inhibits the coil A from beingexcited. At this time, the transistor N1 is turned on, but may be turnedoff.

The order in which the third drive pulse SP73 a and the third drivepulse 73 b are repeated in the third drive pulse SP73 is notparticularly limited. In the example described here, the third drivepulse SP73 a is first applied, and the third drive pulse 73 b is thenapplied, which is repeated subsequently in the same manner, but theorder may be reversed. Further, the third drive pulse SP73 a, the thirddrive pulse SP73 b, the third drive pulse SP73 b, and the third drivepulse SP73 a may be applied in the stated order to be repeatedsubsequently in the same manner. It is desired to equalize the totalperiod occupied by the third drive pulse SP73 a and the total periodoccupied by the third drive pulse 73 b within the segments of the thirddrive pulse SP73 so that magnetic forces excited by the coil A and thecoil B become equal to each other. However, the total periods may differfrom each other within such a range that the magnetic forces excited bythe coil A and the coil B are practically equal to each other. Further,the lengths of the third drive pulse SP73 a and the third drive pulse 73b are desired to be set equal to each other in terms of ease of formingthe third drive pulse SP73, but may not necessarily match each other.

In this manner, each of the transistors of the driver circuit 80 isON/OFF controlled based on the three drive pulses, namely, the first tothird drive pulses SP71 to SP73 of the high-speed drive pulse trainSP70, to thereby excite the coils A and B of the stepper motor 20.

[Description of Rotational Drive by 360° Per Step in Fifth Embodiment:FIGS. 22]

The high-speed rotational drive of the stepper motor 20 in increments of360° per step in the fifth embodiment is described with reference toFIG. 22. First, FIG. 22(a) is an illustration of a state in which thefirst drive pulse SP71 of the high-speed drive pulse train SP70 issupplied to the stepper motor 20. The coil B is excited in the directionindicated by the arrow, and hence the second magnetic-pole portion 22 bis magnetized to the N-pole, while the third magnetic-pole portion 22 cis magnetized to the S-pole. Meanwhile, the coil A is not magnetized,and hence the first magnetic-pole portion 22 a has the S-pole in thesame manner as the third magnetic-pole portion 22 c. Therefore, therotor 21 is rotated in the counterclockwise direction, and the N-pole ofthe rotor 21 is rotated in the counterclockwise direction from thestationary position of 0° to reach the position of about 135°.

Next, as illustrated in FIG. 22(b), when the second drive pulse SP72 issupplied, both the coil A and the coil B are excited in the directionindicated by the arrow. Thus, the first magnetic-pole portion 22 a ismagnetized to the N-pole, the second magnetic-pole portion 22 b ismagnetized to the S-pole, and the third magnetic-pole portion 22 c isnot magnetized. As a result, the rotor 21 is further rotated in thecounterclockwise direction, the N-pole of the rotor 21 is rotated toreach the position of about 270°.

In addition, the third drive pulse SP73 is supplied. The third drivepulse SP73 is formed of the third drive pulse SP73 a and the third drivepulse SP73 b. FIG. 22(c) is an illustration of a state in which thethird drive pulse SP73 a is supplied. The coil A is excited in thedirection indicated by the arrow, and hence the first magnetic-poleportion 22 a is magnetized to the S-pole, while the second magnetic-poleportion 22 b and the third magnetic-pole portion 22 c are magnetized tothe N-pole. Further, FIG. 22(d) is an illustration of a state in whichthe third drive pulse SP73 b is supplied. The coil B is excited in thedirection indicated by the arrow, and hence the second magnetic-poleportion 22 b is magnetized to the S-pole, while the first magnetic-poleportion 22 a and the third magnetic-pole portion 22 c are magnetized tothe N-pole.

Then, in the segments of the third drive pulse SP73, the third drivepulse SP73 a and the third drive pulse SP73 b are repeatedly applied atshort intervals, and hence the magnetization state illustrated in FIG.22(c) and the magnetization state illustrated in FIG. 22(d) repeatedlyappear. An effective magnetization state that appears in the steppermotor 20 can be assumed to be obtained by combining the twomagnetization states. As a result, the third magnetic-pole portion 22 cis magnetized to the N-pole in the same manner as in the magnetizationstates illustrated in FIG. 22(c) and FIG. 22(d), and therefore has theN-pole over all the segments of the third drive pulse SP73. Meanwhile,different poles alternately appear in the first magnetic-pole portion 22a and the second magnetic-pole portion 22 b, and hence the magnetizationstates are apparently canceled, which results in effectivelydemagnetized state, namely, a weakly magnetized state. With this, therotor 21 is further rotated in the counterclockwise direction, and theN-pole of the rotor 21 is rotated to reach the position of about 360°.

In this manner, it is possible to achieve the rotational drive by 360°through one-step drive based on the high-speed drive pulse train 70formed of the three drive pulses SP71 to SP73.

In the third embodiment, the magnetization state of the third drivepulse SP73, which is obtained by combining the magnetization stateillustrated in FIG. 22(c) and the magnetization state illustrated inFIG. 22(d) at this time is substantially the same as that illustrated inFIG. 14(e). However, as apparent from FIG. 22, the coil A and the coil Bare not simultaneously excited, and hence in order to supply asufficient rotational force to the rotor 21, the length of the thirddrive pulse SP73 may be set longer than those of the first drive pulseSP71 and the second drive pulse SP72.

In this manner, with the electronic watch according to the fifthembodiment, even when the coil terminals O2′ of the coil A and the coilB are short-circuited to be used in common, it is possible to performthe rotational drive by 360° in one step by supplying the high-speeddrive pulse train SP70 formed of the three drive pulses SP71 to 73. Inthis case, it suffices that the number of drive waveforms to be suppliedis three and that the number of transistors is smaller than that in thefirst embodiment, which is effective in miniaturization of the circuitscale and reduction in cost.

Further, the rotational drive by 360° through one-step drive in thefifth embodiment may replace the rotational drive by 360° per step inthe high-speed drive mode in the third embodiment. With thisconfiguration, it is possible to achieve the rotational drive by 360°per step in the high-speed drive mode in addition to the rotationaldrive by 180° per step in the normal drive mode. In addition, in therotational drive by 360° through one-step drive in the fifth embodiment,the coil A and the coil B are not simultaneously excited, and themaximum value of the current consumption can be suppressed to a lowlevel. Therefore, the high-speed drive based on the rotational drive by360° per step can be performed even when a power source condition isstrict, for example, when the outside temperature is low or in a statein which the power supply voltage is lowered.

Sixth Embodiment

[Description of Configuration of Electronic Watch According to SixthEmbodiment: FIG. 23]

Next, a schematic configuration of an electronic watch according to asixth embodiment of the present invention is described with reference toFIG. 23. Reference symbol 90 denotes an analog indication-typeelectronic watch according to the sixth embodiment. The electronic watch90 includes, as basic components, an oscillation circuit 92 configuredto output the reference signal P1, a control circuit 93 configured toreceive the reference signal P1 as input and to output control signalsCN7, CN8, CN9, and CN10, two high-speed drive pulse generation circuits,namely, a high-speed drive pulse generation circuit (variable portion)94 and a high-speed drive pulse generation circuit (fixed portion) 95, acorrection pulse generation circuit 96, a detection pulse generationcircuit 97, a pulse selection circuit 16, a driver circuit 100, and thestepper motor 20, and further includes a rotation detectiondetermination circuit 91.

The high-speed drive pulse generation circuit (variable portion) 94 andthe high-speed drive pulse generation circuit (fixed portion) 95 receivethe control signals CN7 and CN8, respectively, as input, and generatesand outputs SP30 and SP40, respectively, being parts of the high-speeddrive pulse train formed of a plurality of drive pulses for driving thestepper motor 20.

The correction pulse generation circuit 96 receives the control signalCN9 as input, and generates and outputs a correction pulse FP fordriving the stepper motor 20.

The detection pulse generation circuit 97 receives the control signalCN10 as input, and generates and outputs the detection pulse CP fordetecting that the rotor 21 of the stepper motor 20 has been rotated ina normal state.

The pulse selection circuit 16 selects the pulses SP30, SP40, FP, andCP, which are generated and output by the high-speed drive pulsegeneration circuit (variable portion) 94 and the high-speed drive pulsegeneration circuit (fixed portion) 95, the correction pulse generationcircuit 96, and the detection pulse generation circuit 97, respectively,and outputs the pulses SP30, SP40, FP, and CP to the driver circuit 100at an appropriate timing.

The driver circuit 100 supplies the drive waveforms O1 to O4 to the coilA and the coil B of the stepper motor 20 based on the pulses input fromthe pulse selection circuit 16 to drive the stepper motor 20.

The rotation detection determination circuit 91 detects an inducedcurrent due to the free rotation of the rotor 21 of the stepper motor 20based on detection signals CS detected when the detection pulse CP issupplied to the coil A and the coil B of the stepper motor 20 todetermine the presence or absence of the rotation of the rotor 21, andoutputs a determination result CK. The output determination result CK isinput to the pulse selection circuit 16 to be used for the switchingcontrol of the pulse.

[Description of Circuit Configuration of Driver Circuit in SixthEmbodiment: FIG. 24]

Next, with reference to FIG. 24, description is given of an example ofthe circuit configuration of the driver circuit 100 configured to drivethe stepper motor 20. The driver circuit 100 is formed of four buffercircuits configured to supply four drive waveforms to the coil A and thecoil B of the stepper motor 20.

As illustrated in FIG. 24, buffer circuits including the transistors P1to 4 being the P-channel MOS transistors and the transistors N1 to 4being the N-channel MOS transistors, which are complementarily connectedto each other, are connected to the coil terminals O1 to O4 of the coilA and the coil B, and are configured to output the drive waveforms O1 toO4, respectively.

In addition, transistors TP1 and TP2 being P-channel MOS transistors areconnected to the coil terminals O1 and O2, respectively, of the coil Avia detection resistances, and transistors TP3 and TP4 being P-channelMOS transistors are connected to the coil terminals O3 and O4,respectively, of the coil B via detection resistances. The detectionpulse CP is output to the transistors TP1 to TP4, and the detectionsignals CS obtained thereby are input to the rotation detectiondetermination circuit 91.

[Description of Rotation Detection in Sixth Embodiment: FIG. 25 andFIGS. 26]

Now, the rotation detection of the rotor 21 of the stepper motor 20 bythe detection pulse CP and the rotation detection determination circuit91 is described with reference to FIG. 25 and FIG. 26.

FIG. 25 is a diagram for illustrating a structure of the stepper motor20. A stator of the stepper motor 20 includes the first magnetic-poleportion 22 a and the second magnetic-pole portion 22 b, which are formedso as to oppose to each other through the rotor 21, and the thirdmagnetic-pole portion 22 c, which is formed between the firstmagnetic-pole portion 22 a and the second magnetic-pole portion 22 b soas to oppose to the rotor 21. There are provided the coil A so as toform a magnetic circuit between the first magnetic-pole portion 22 a andthe third magnetic-pole portion 22 c and the coil B so as to form amagnetic circuit between the second magnetic-pole portion 22 b and thethird magnetic-pole portion 22 c.

A constriction portion 23, in which the stator has a small width, isprovided between the first magnetic-pole portion 22 a and the secondmagnetic-pole portion 22 b on the opposite side of the thirdmagnetic-pole portion 22 c through the rotor 21. In addition, adirection of the third magnetic-pole portion 22 c is set as 0° whenviewed from the center of the rotor 21, and slits 24 are formed atpositions on the left and right by about 75°. The slits 24 are formed sothat the first magnetic-pole portion 22 a and the third magnetic-poleportion 22 c are not directly magnetically connected to each other andthe second magnetic-pole portion 22 b and the third magnetic-poleportion 22 c are not directly magnetically connected to each other. Theslit 24 may be formed as a gap as illustrated here, or a non-magneticmaterial having a small width may be inserted into the position of theslit 24 to be combined with the stator.

With the constriction portion 23 and the slits 24 being thus provided,magnetism generated in the stator due to electromagnetic induction whilethe rotor 21 is rotated by being supplied with a drive pulse and whilethe rotor 21 is freely rotated due to the inertia of the rotor 21becomes hard to pass through the slits 24 and the constriction portion23 having large magnetic resistance, and hence a large part of themagnetism follows a path passing through the coil A or the coil B. Withthis, the use of the coil A or the coil B increases detectionsensitivity exhibited when the induced current, which is induced by therotation of the rotor 21, is detected through use of the coil A or B.

That is, by turning on the transistors TP1 to TP4 illustrated in FIG. 24based on the detection pulse CP at a predetermined timing, it ispossible to extract magnitudes of the induced currents generated in thecoil terminals O1 to O4 corresponding to the respective transistors asthe detection signals CS being voltage signals. The rotation detectiondetermination circuit 91 determines the rotation or non-rotation of therotor 21 based on the detection signal CS, and outputs the determinationresult CK.

Now, the rotation and non-rotation of the rotor 21 are described. FIG.26 are diagrams for illustrating the rotation and non-rotation of therotor 21 of the stepper motor 20. FIG. 26(a) is an illustration of acase of the non-rotation of the rotor 21, that is, a case in which therotor 21 fails to be rotated without being rotated by a desired angleeven when the drive pulse is applied. In this case, the drive pulse isoutput to temporarily rotate the rotor 21 in the counterclockwisedirection, but due to an insufficient drive force, the rotor 21 isreturned to the initial position of 0° by being reversely rotated in theclockwise direction by a holding torque. In this case, the rotor 21finally fails to be rotated, which is referred to as “non-rotation”. InFIG. 26(a), the rotation of the rotor 21 during a period in which thedrive pulse is being output is indicated by the broken line.

FIG. 26(b) is an illustration of a case of the rotation of the rotor 21,that is, a case in which the rotor 21 is successfully rotated by adesired angle due to the applied drive pulse. In this case, the drivepulse is output to rotate the rotor 21 in the counterclockwise directionby an angle equal to or larger than a given angle. Thus, the rotor 21 isfurther rotated in the counterclockwise direction by a holding torqueeven after the drive pulse stops being output, and rotated to reach theposition of 180° being a target position of the rotation per step. Inthis case, the rotor 21 is rotated to finally reach the target positionof the rotation per step, which is referred to as “rotation”.

In this manner, the rotor 21 differs in behavior of the rotor 21 afterthe output of the drive pulse between the case of the rotation and thecase of the non-rotation, and hence the waveforms of the inducedcurrents generated in the coil A and the coil B differ from each other.The different waveforms are extracted as the detection signals CS basedon the detection pulse CP, and the rotation detection determinationcircuit 91 determines the rotation or non-rotation of the rotor.

[Description of Generation of Drive Pulse and Drive Waveform in SixthEmbodiment: FIG. 27]

With reference to FIG. 27, description is given of an example of thedrive waveform of a high-speed drive pulse for rotationally driving thestepper motor in the sixth embodiment in increments of 360° per step.The drive waveform itself described here is the same as that describedin the first embodiment with reference to FIG. 6.

However, in the sixth embodiment, the high-speed drive pulse train ishandled by being divided into the variable drive pulse SP30 being thefirst half and the fixed drive pulse SP40 being the second half. Theentire high-speed drive pulse train illustrated in FIG. 27 is the sameas that illustrated and shown in FIG. 6, and the three drive pulsesSP11, SP12, and SP13 that form the high-speed drive pulse train are thesame as those of the first embodiment and are denoted by the samereference symbols.

In this case, the variable drive pulse SP30 corresponds to the drivepulse 11. As described later, the variable drive pulse SP30 has thelength (period) changed depending on a condition. Meanwhile, the fixeddrive pulse SP40 corresponds to the drive pulse 12 and the drive pulseSP13. The length of the fixed drive pulse SP40 is fixed and determinedin advance.

The operation of each of the transistors of the driver circuit 80configured to output the drive pulses SP11 to 13, which form thevariable drive pulse SP30 and the fixed drive pulse SP40, is the same asthat described in the first embodiment with reference to FIG. 6, andhence duplicate description is omitted here.

[Description of Pulse Waveforms in Sixth Embodiment: FIG. 28]

FIG. 28 is an illustration of the pulse waveforms in the sixthembodiment. In FIG. 28, waveforms (1) to (3) are illustrated as examplesof drive pulses to be applied to the stepper motor 20 when the rotationof the rotor 2 l is determined, that is, examples of the variable drivepulse SP30 and the fixed drive pulse SP40. Which of pulse waveformsincluding the waveforms (1) to (3) is to be selected varies depending onthe result of the rotation detection. Further, a waveform (4) indicatesthe correction pulse FP to be applied to the stepper motor 20 when thenon-rotation of the rotor 21 is determined. A waveform (5) indicates atiming to apply the detection pulse CP for performing the rotationdetection.

In the sixth embodiment, the length of the variable drive pulse SP30 canbe selected from among the five lengths of from 1 ms to 5 ms in units of1 ms, and the fixed drive pulse SP40 is output for 3.5 ms immediatelyafter the variable drive pulse SP30. The rotation detection isperformed, and it is determined based on a result of the detection whichof the lengths of the variable drive pulse is to be selected. This isdescribed later in more detail, but the basic idea is that the variabledrive pulse SP30 is kept being output until the rotation is determined.

When the rotation cannot be determined even after the variable drivepulse SP30 having the maximum length (5 ms) is output, the correctionpulse FP indicated by the waveform (4) is output to reliably rotate therotor 21. The correction pulse FP is output to reliably rotate the rotor21 when the non-rotation of the rotor 21 is determined, and has thewaveform set so as to have a strong drive force. In this case, thewaveform is set to be continuously output for 5 ms and then continue thepulse output for 4 ms every 0.25 ms with a duty cycle of 8/16.

The detection pulse CP is set as a pulse having a width of 16 μs, whichis output every 0.5 ms after an elapse of 0.25 ms from the start of theoutput of the variable drive pulse SP30 until an elapse of 4.75 ms.

The lengths and shapes of the variable drive pulse SP30, the fixed drivepulse SP40, and the correction pulse FP, the output timing of thedetection pulse CP, and the like in the above description are merelyexamples, and may be changed depending on different kinds ofconfigurations including the shape and size of the stepper motor 20 andadditions mounted to the stepper motor 20.

[Description of Flow of High-Speed Drive Pulse Train Output in SixthEmbodiment: FIG. 29]

FIG. 29 is a flow chart for illustrating an operation for high-speeddrive pulse train output in the sixth embodiment. Now, with reference tothis flow chart, description is given of the operation of the electronicwatch 90 according to the sixth embodiment, which is controlled by thecontrol circuit 93.

First, at the timing of hand movement, the variable drive pulse SP30output by the high-speed drive pulse generation circuit (variableportion) is selected by the pulse selection circuit 16 to be output tothe driver circuit 100 (Step ST1). With this, the rotor 21 of thestepper motor 20 starts the rotation. Then, the detection pulse CP,which is output from a detection pulse generation circuit every 5 msafter an elapse of 0.25 ms, is selected by the pulse selection circuit16 to be output to the driver circuit 100, and the rotation detection isstarted (Step ST2). The rotation detection determination circuit 91outputs the determination result CK based on the detection signal CSobtained as a result of the detection.

In this case, the determination of the rotation or non-rotationperformed by the rotation detection determination circuit 91 isdescribed with reference to FIG. 30. FIG. 30 is a diagram forillustrating waveforms of induced currents generated in the coil A andthe coil B when the variable drive pulse SP30 is applied andillustrating pulses applied to the coil terminals O1 to O4 and detectionsignals.

The variable drive pulse SP30 has been applied to the coil terminal O3since the time 0 ms, and a voltage is applied between the coil terminalsO3 and O4 of the coil B to excite the coil B. This causes the rotor 21to start the rotation to generate a positive-direction induced currentbetween the coils A and B.

The detection pulse CP is applied to the coil A being a coil differentfrom the coil to which the variable drive pulse SP30 is applied.Specifically, the detection pulse CP is applied to the coil terminal O1every 0.5 ms after 0.25 ms from the start, to thereby obtain thedetection signal CS corresponding to each detection pulse CP.

As apparent from the waveform of the induced current generated in thecoil A of FIG. 30, at the beginning of the rotation of the rotor 21, theinduced current generated in the coil A has a value that has a positivesign and is not so large. Depending on the condition, in the exampleillustrated here, the sign of the induced current is reversed at a timepoint at which about 2.5 ms have elapsed from the start of the rotationto become a negative sign, which generates a trough of a waveformindicating a value having a magnitude equal to or larger than a fixedmagnitude.

This trough of the waveform having a negative value indicates that therotor 21 has overcome the peak of potential to be rotated toward thestatically stable point being a target, and it is possible to detect therotation by detecting this trough of the waveform having a negativesign, which is indicated by the hatched portion in FIG. 30.

The detection signal CS detected from the coil terminal O1 is comparedwith a predetermined negative threshold value th. Then, as illustratedin FIG. 30, in this example, the detection signal CS does not fall belowthe threshold value th and is thus not obtained until CP2.75 after anelapse of 2.75 ms from the start of the rotation, but the detectionsignal CS that falls below the threshold value th is obtained based onthe detection pulse CP3.25 after an elapse of 3.25 ms.

Then, in the sixth embodiment, the rotation is determined when twoconsecutive detection signals CS are obtained, and hence the rotationdetection determination circuit 91 is configured to determine therotation when the detection signal CS based on the detection pulseCP3.75 after an elapse of 3.75 ms from the start of the rotation isfurther detected, and to output the determination result CK. Meanwhile,when two consecutive detection signals CS are not obtained even after4.75 ms have elapsed from the start of the rotation, the rotationdetection determination circuit 91 determines the non-rotation andoutputs the determination result CK.

A timing at which consecutive detection signals CS are obtained differsdepending on different kinds of conditions including the power supplyvoltage, the magnitude of the load, and the attitude of the electronicwatch 90. Further, the condition for the determination is not limited tothe two consecutive signals, and the condition may be freely set. Forexample, the rotation may be determined based on one signal or three ormore signals, or the rotation may be determined based on consecutivesignals or a number obtained by adding the numbers of signals obtainedwithin a predetermined period.

Referring back to FIG. 29, after the rotation detection is started, thetiming at which the rotation determination is made is monitored. Thatis, first, it is determined whether or not the detection signal CS hasbeen obtained two times until 0.75 ms have elapsed since the rotationwas started (Step ST31). When the detection signal CS has been obtainedtwo times (Step ST31: Y), the rotation detection is ended (Step ST41) tostop outputting the detection pulse CP, and sets the width of thevariable drive pulse SP30 to 1 ms (Step ST51). With this, the variabledrive pulse SP30 stops being output in 1 ms, and the fixed drive pulseSP40 is subsequently output (Step ST7), which brings the rotation perstep of the rotor 21 to an end.

When the detection signal CS has not been obtained two times until 0.75ms have elapsed since the rotation was started (Step ST31: N), it issubsequently determined whether or not the detection signal CS has beenobtained two times until 1.75 ms have elapsed (Step ST32). When thedetection signal CS has been obtained two times (Step ST32: Y), therotation detection is ended (Step ST42), and the width of the variabledrive pulse SP30 is set to 2 ms (Step ST53). After the variable drivepulse SP30 stops being output, the fixed drive pulse SP40 issubsequently output (Step ST7).

Similarly, when the detection signal CS has not been obtained two timesuntil 1.75 ms have elapsed since the rotation was started (Step ST32:N), it is subsequently determined whether or not the detection signal CShas been obtained two times until 2.75 ms have elapsed (Step ST33). Whenthe detection signal CS has been obtained two times (Step ST33: Y), therotation detection is ended (Step ST43), and the width of the variabledrive pulse SP30 is set to 3 ms (Step ST53). After the variable drivepulse SP30 stops being output, the fixed drive pulse SP40 issubsequently output (Step ST7).

Similarly, when the detection signal CS has not been obtained two timesuntil 2.75 ms have elapsed since the rotation was started (Step ST33:N), it is subsequently determined whether or not the detection signal CShas been obtained two times until 3.75 ms have elapsed (Step ST34). Whenthe detection signal CS has been obtained two times (Step ST34: Y), therotation detection is ended (Step ST44), and the width of the variabledrive pulse SP30 is set to 4 ms (Step ST54). After the variable drivepulse SP30 stops being output, the fixed drive pulse SP40 issubsequently output (Step ST7).

Similarly, when the detection signal CS has not been obtained two timesuntil 3.75 ms have elapsed since the rotation was started (Step ST34:N), it is subsequently determined whether or not the detection signal CShas been obtained two times until 4.75 ms have elapsed (Step ST35). Whenthe detection signal CS has been obtained two times (Step ST35: Y), therotation detection is ended (Step ST45), and the width of the variabledrive pulse SP30 is set to 5 ms (Step ST55). After the variable drivepulse SP30 stops being output, the fixed drive pulse SP40 issubsequently output (Step ST7).

Then, the non-rotation is determined when the detection signal CS hasnot been obtained two times until 4.75 ms have elapsed since therotation was started (Step ST54: N), and hence the correction pulse FPis output (Step ST6) to reliably rotate the rotor 21.

In this example, the width of the variable drive pulse SP30 is set infive steps ranging from 1 ms to 5 ms in units of 1 ms, but may be setmore finely (or roughly), or the output of the variable drive pulse SP30may be stopped immediately after the rotation determination is made tooutput the fixed drive pulse SP40. Further, the variable drive pulseSP30 may be output again immediately after the fixed drive pulse SP40 isoutput or after a given period (for example, 1 ms) have elapsed sincethe fixed drive pulse SP40 was output, to thereby eliminate a dead timeto rotate the rotor 21 at high speed.

In this manner, with the electronic watch according to the sixthembodiment, the rotation or non-rotation of the rotor 21 can be detectedin the case of performing the rotational drive by 360° in one step, andit is possible to reliably rotate the rotor 21 by outputting thecorrection pulse FP in the case of the non-rotation. Further, the lengthof the high-speed drive pulse train to be output is only required to bea length required for rotating the rotor 21. Therefore, the powerconsumption is reduced, and a dead time is eliminated to enable thehigh-speed drive.

Modification Example 1 of Sixth Embodiment: FIG. 31

In the sixth embodiment, the output waveforms of the variable drivepulse SP30 and the fixed drive pulse 40 are as illustrated in FIG. 28,but the pulse shapes of those waveforms may be further deformed based onthe power supply voltage. FIG. 31 is an illustration of pulse waveformsafter the deformation, in which the variable drive pulses SP30 and thefixed drive pulses 40 indicated by waveforms (1) to (3) are notcontinuously output pulses (full pulses) but are pulses whose on and offare switched over at a given cycle (chopper pulses). In the exampleillustrated in FIG. 31, the duty cycle of the chopper pulse is 8/16 sothat the on and off of the output are repeatedly switched over at acycle of 0.25 ms.

The pulse waveform based on the chopper pulse has the power consumptionreduced by an amount corresponding to the suppressed output. On theother hand, output is lowered, and hence the non-rotation is liable tooccur. In view of this, the chopper pulses illustrated in FIG. 31 may beused to achieve reduction in power consumption due to a sufficient driveforce when the power supply voltage is high, namely, has a value equalto or larger than a predetermined value (for example, is 2.5 V orhigher), while the rotor 21 may be stably rotated through use of thefull pulses illustrated in FIG. 28 when the power supply voltage has avalue smaller than a predetermined value (for example, is lower than 2.5V).

With this configuration, only by turning on or off the signal at apredetermined cycle in the final stage of outputting a pulse to thedriver circuit, it is possible to apply a plurality of kinds of drivepulses different in power consumption and in output to the stepper motor20, and hence it is not required to separately provide the variabledrive pulse SP30 and the fixed drive pulse SP40. The duty cycle of thechopper pulse is freely set, and three or more kinds of pulse waveformsmay be provided based on the power supply voltage. Further, the variabledrive pulse SP30 and the fixed drive pulse SP40 may be set to havedifferent duty cycles and different cycle periods.

The correction pulse FP is required to have a strong drive force inorder to reliably rotate the rotor 21, and hence it is undesirable tolimit the output by using a chopper pulse. However, when the rotor 21 isexpected to be reliably rotated depending on a power supply voltage orother such condition, the chopper pulse may be used within that range inthe same manner as in the cases of the variable drive pulse SP30 and thefixed drive pulse SP40.

Modification Example 2 of Sixth Embodiment: FIG. 32

In Modification Example 1 of the sixth embodiment, the duty cycle of thechopper pulse having a pulse waveform deformed based on the power supplyvoltage may be further changed with an elapse of time. FIG. 32 is anillustration of a part of the pulse waveform in Modification Example 2of the sixth embodiment, in which a waveform (1) includes the variabledrive pulse SP30 having a length of 1 ms, a waveform (2) includes thevariable drive pulse SP30 having a length of 2 ms, and a waveform (3)includes the variable drive pulse SP30 having a length of 3 ms. Theillustrations of waveforms including the variable drive pulses SP30having lengths of 4 ms and 5 ms are omitted.

The basic idea employed here is that a drive pulse for generating astronger drive force is supplied as the time taken until the rotationdetermination is made becomes longer. That is, it is conceivable thatthe rotation determination can be made at an early timing when the powersupply voltage is high and the drive force is sufficient, and that theduty cycle may be lowered for the reduction in power consumption inorder to avoid unnecessary power consumption. Meanwhile, it isconceivable that the time taken until the rotation determination is madebecomes longer as the power supply voltage is lowered with a lesssufficient drive force, and that it is required to supply a drive pulsehaving a sufficient drive force in order to avoid the non-rotation.

In view of this, in Modification Example 2 of the sixth embodiment, thevariable drive pulse SP30 based on a chopper pulse having a low dutycycle of 8/16 is first applied to the stepper motor 20 during the firstperiod of 1 ms from the start of the rotation. When the rotationdetermination is made through this operation, the waveform (1) isobtained, and it turns out that the drive force is sufficient, whichcauses the fixed drive pulse SP40 to have as low a duty cycle as 2/16.Further, the period itself of the fixed drive pulse SP40 may be set asshort as a total of 1 ms including 0.75 ms for the second drive pulse 12and 0.25 ms for the third drive pulse.

Unless the rotation determination is made in 1 ms from the start of therotation, the duty cycle of the variable drive pulse SP30 is increasedto raise the drive force. Specifically, the duty cycle of the chopperpulse is set to 10/16. When the rotation determination is made throughthis operation, the waveform (2) is obtained. In this case, the driveforce is taken into consideration to set the duty cycle of the fixeddrive pulse SP40 to 4/16, which is stronger than in the case of thewaveform (1). Further, the period of the fixed drive pulse SP40 may beset to a total of 1.5 ms including 1 ms for the second drive pulse 12and 0.5 ms for the third drive pulse, which is longer than in the caseof the waveform (1).

Further, unless the rotation determination is made in 2 ms from thestart of the rotation, the duty cycle of the variable drive pulse SP30is further increased to raise the drive force. Specifically, the dutycycle of the chopper pulse is set to 12/16. When the rotationdetermination is made through this operation, the waveform (3) isobtained. Then, the drive force is taken into consideration to set theduty cycle of the fixed drive pulse SP40 to 6/16, which is stronger thanin the case of the waveform (2). Further, the period of the fixed drivepulse SP40 may be set to a total of 2 ms including 1.25 ms for thesecond drive pulse 12 and 0.75 ms for the third drive pulse, which islonger than in the case of the waveform (2).

Subsequently, in the same manner, each time one of 3 ms and 4 ms haveelapsed since the rotation was started, the duty cycle of the variabledrive pulse SP30 is increased, and the duty cycle of the fixed drivepulse SP40 is also increased simultaneously. At this time, the length ofthe fixed drive pulse SP40 may also be increased simultaneously. Withthis operation, when the drive force is sufficient, useless powerconsumption is reduced. Meanwhile, as the drive force becomes lesssufficient with a decrease in power supply voltage, a more time isrequired from the start of the rotation until the rotation determinationis made, and hence the duty cycle of the drive pulse to be applied isincreased with an elapse of time from the start of the rotation, tothereby reduce the risk of causing the non-rotation. That is, it ispossible to prevent such a situation that a failure in rotation due toreduction in drive force ascribable to the change to the chopper pulsecauses the correction pulse FP to be frequently output to ratherincrease the power consumption. With this, it is possible to achievereduction in the power consumption and stable rotation of the rotor 21with a satisfactory balance.

In the example illustrated in FIG. 32, both the duty cycle and thelength of the fixed drive pulse SP40 are changed, but anyone thereof maybe changed. For example, only the duty cycle may be changed with thelength being fixed, or only the length may be changed with the dutycycle being fixed.

Seventh Embodiment

An electronic watch according to a seventh embodiment of the presentinvention basically has the same structure and control as those of theelectronic watch 1 according to the first embodiment. Therefore, thematters described with reference to FIG. 1 to FIG. 7 also apply to theelectronic watch according to the seventh embodiment.

In the seventh embodiment, the drive pulse at the time of the drive by360° per step is switched based on the power supply voltage and thetemperature of the electronic watch. That is, referring to FIG. 7, inthe high-speed drive by 360° per step, both the coil A and the coil Bare excited in the state of FIG. 7(b). In this case, about twice thecurrent is required compared with the case of exciting the coil A or thecoil B independently.

Meanwhile, as illustrated and shown in FIG. 4 and FIG. 5, the coil A andthe coil B are not simultaneously excited in the normal drive by 180°per step.

In this case, when a large amount of electricity is instantaneouslyconsumed, temporary reduction in power supply voltage is caused. Thereis no problem when the condition is satisfactory with the power supplyvoltage being satisfactorily sufficient. However, when the power storageamount decreases to lower the power supply voltage itself or under acondition that the power supply voltage is liable to be temporarilylowered with the temperature being low, there is a possibility that thetemporary reduction in power supply voltage at the time of thehigh-speed drive by 360° per step, which is illustrated in FIG. 7, maybecome a problem.

In view of this, in the seventh embodiment, as the waveform at the timeof the high-speed drive by 360° per step, two kinds of waveforms,namely, that illustrated in FIG. 7 and a drive waveform for a lowcurrent, which is to be used when there is a fear of the temporaryreduction in power supply voltage, for example, when the power supplyvoltage has a value equal to or smaller than a given value or when thetemperature of the electronic watch is equal to or lower than a givenlevel, are provided, and are switched over based on the power supplyvoltage or the temperature of the electronic watch.

[Description of Drive Waveform for Low Current of Drive Pulse in SeventhEmbodiment: FIG. 33]

FIG. 33 is a diagram for illustrating a high-speed drive pulse trainSP80 being an example of the drive waveform of the drive pulse in theseventh embodiment. First, the high-speed drive pulse train SP80 is usedfor rotationally driving the rotor of the stepper motor 20 of FIG. 2from the stationary position of 0° in the forward rotation direction(counterclockwise) in increments of 360°. FIG. 33 is an illustration ofa drive waveform based on the high-speed drive pulse SP80 and the fourdrive waveforms O1, O2, O3, and O4 to be output from the driver circuit10.

In FIG. 33, the high-speed drive pulse train SP80 to be output from thehigh-speed drive pulse generation circuit 4 is, in this example, a pulsetrain composed of 3 bits, namely, SP81 to SP83 and formed of the threedrive pulses, namely, the first drive pulse SP81, the second drive pulseSP82, and the third drive pulse SP83 in time series, which includes alogical “1” or a logical “0” in order to turn on/off each of thetransistors of the driver circuit 80.

In the first drive pulse SP81, the drive waveform O3 has a voltage ofless than 0 V, and the other drive waveforms O1 to O3 have a voltage of0 V. With this, a drive current flows into the coil B of the steppermotor 20 connected to the coil terminals O3 and O4 to excite the coil B.

Further, in the second drive pulse SP82, the drive waveform O2 has avoltage of less than 0 V, and the drive waveforms O1, O3, and O4 have avoltage of 0 V. With this, a drive current flows into the coil A of thestepper motor 20 connected to the coil terminals O1 and O2 to excite thecoil A.

Further, in the third drive pulse SP83, the drive waveform O4 has avoltage of less than 0 V, and the other drive waveforms O1 to O3 have avoltage of 0 V. With this, a drive current flows into the coil B of thestepper motor 20 connected to the coil terminals O3 and O4 to excite thecoil B.

[Description of Rotational Drive by 360° Per Step Based on DriveWaveform for Low Current in Seventh Embodiment: FIGS. 34]

With reference to FIG. 34, description is given of the high-speedrotational drive in increments of 360° per step based on the drivewaveform for a low current, which is performed by the stepper motor 20in the seventh embodiment. First, FIG. 34(a) is an illustration of astate in which the first drive pulse SP81 of the high-speed drive pulsetrain SP80 is supplied to the stepper motor 20. The coil B is excited inthe direction indicated by the arrow, and hence the second magnetic-poleportion 22 b is magnetized to the N-pole, while the third magnetic-poleportion 22 c is magnetized to the S-pole. Meanwhile, the coil A is notmagnetized, and hence the first magnetic-pole portion 22 a has theS-pole in the same manner as the third magnetic-pole portion 22 c.Therefore, the rotor 21 is rotated in the counterclockwise direction,and the N-pole of the rotor 21 is rotated in the counterclockwisedirection from the stationary position of 0° to reach the position ofabout 135°.

Next, as illustrated in FIG. 34(b), when the second drive pulse SP62 issupplied, both the coil A is excited in the direction indicated by thearrow. Thus, the first magnetic-pole portion 22 a is magnetized to theN-pole, and the second magnetic-pole portion 22 b and the thirdmagnetic-pole portion 22 c are magnetized to the S-pole. As a result,the rotor 21 is further rotated in the counterclockwise direction, andthe N-pole of the rotor 21 is rotated to reach the position of about225°.

Further, as illustrated in FIG. 34(c), when the third drive pulse SP83is supplied, the coil B is excited in the direction indicated by thearrow. Thus, the second magnetic-pole portion 22 b is magnetized to theS-pole, and the first magnetic-pole portion 22 a and the thirdmagnetic-pole portion 22 c are magnetized to the N-pole. As a result,the rotor 21 is further rotated in the counterclockwise directionwithout stopping, and the N-pole of the rotor 21 is rotated to reach theposition of about 315°.

After that, as illustrated in FIG. 34(d), when the supply of thehigh-speed drive pulse train SP80 is ended, the coil terminals O1 to O4all have a voltage of 0 V. Thus, the coil A and the coil B stop beingexcited, which cancels the magnetization of the first to thirdmagnetic-pole portions, but the rotor 21 continues to rotate untilreaching the statically stable point of 360° (0°) without stopping, andis held at that position. In this manner, the stepper motor 20 can berotationally driven by 360° through one-step drive based on thehigh-speed drive pulse train 80 formed of the three drive pulses SP81 toSP83.

In the drive based on the high-speed drive pulse train SP80 being thedrive waveform for a low current in the seventh embodiment, it isrequired to rotate the rotor 21 by 90° from the position of 225° in FIG.34(b) to the position of 315° in FIG. 34(c), but this rotation isperformed by exciting a single coil, and hence the drive force isslightly inferior to that of the high-speed drive pulse train SP10 forthe high-speed drive, which is illustrated and shown in FIG. 6.Therefore, it tends to take a slightly more time to rotate the rotor 21based on the high-speed drive pulse train SP80.

Meanwhile, as apparent from FIG. 34, in the high-speed drive pulse trainSP80 being the drive waveform for a low current, two coils are notsimultaneously excited, and hence the maximum value of the current isabout ½ of the high-speed drive pulse train SP10 illustrated and shownin FIG. 6. Therefore, in the high-speed drive under the condition thatthere is a fear of the temporary reduction in voltage due to largecurrent consumption, the high-speed drive pulse train SP80 being thedrive waveform for a low current is used, and otherwise, the high-speeddrive pulse train SP10 illustrated and shown in FIG. 6 may be used.

The high-speed drive pulse train SP80 may be applied not only to thefirst embodiment but also to the third embodiment. In that case, forexample, the high-speed drive pulse train SP20 illustrated in FIG. 14may be switched by the high-speed drive pulse train SP80 being the drivewaveform for a low current in the seventh embodiment depending on thecondition.

Eighth Embodiment

An electronic watch according to an eighth embodiment of the presentinvention is an example obtained by combining the sixth embodiment andthe seventh embodiment, in which low power consumption and the stabilityof rotation under a poor power source condition, for example, a reducedpower supply voltage or a low temperature are achieved simultaneouslywith higher reliability.

When the high-speed drive pulse train SP in the sixth embodiment, whichis illustrated in FIG. 27, and the high-speed drive pulse train SP80based on the drive waveform for a low current in the seventh embodiment,which is illustrated in FIG. 33, are compared with each other, the firstdrive pulses SP11 and SP81 are used in common. That is, when thehigh-speed drive pulse train SP80 based on the drive waveform for a lowcurrent in the seventh embodiment is divided into the variable drivepulse SP30 formed of the first drive pulse SP81 and a fixed drive pulseSP90 formed of the second and third drive pulses SP82 and SP83, thevariable drive pulse SP30 is used in common in the sixth embodiment andthe seventh embodiment.

Meanwhile, the fixed drive pulse SP40 in the sixth embodiment and thefixed drive pulse SP90 in the seventh embodiment are different drivepulses.

In view of this, in the eighth embodiment, as in the sixth embodiment,the length of the variable drive pulse SP30 is changed based on the timetaken until the rotation determination is made, and the fixed drivepulse is switched to the fixed drive pulse SP90 based on the drivewaveform for a low current when it is determined that the time takenuntil the rotation determination is made is long with the power sourcecondition being poor.

[Description of Flow of High-Speed Drive Pulse Train Output in EighthEmbodiment: FIG. 35]

FIG. 35 is a flow chart for illustrating an operation for high-speeddrive pulse train output in the eighth embodiment. Now, with referenceto this flow chart, description is given of the operation of theelectronic watch according to the eighth embodiment, which is controlledby the control circuit.

In this operation flow, the operations performed in Step ST1, Step ST2,Step ST31 to Step ST35, Step ST41 to Step ST45, Step ST51 to Step ST55,Step ST6, and Step ST7 are the same as those of the flow in the sixthembodiment illustrated in FIG. 29. This operation flow is different fromthe flow illustrated in FIG. 29 only in that Step ST55 is followed byStep ST71 instead of Step ST7.

That is, at the timing of hand movement, the variable drive pulse SP30is output to the driver circuit 100 (Step ST1) to start the rotation ofthe rotor 21 of the stepper motor 20, and then the rotation detection isstarted (Step ST2). When the rotation determination is made in Step ST31to Step ST35, the rotation detection is ended in Step ST41 to Step ST45,and in Step ST51 to Step ST55, the length of the variable drive pulseSP30 is set based on the time taken until the rotation determination ismade. After the execution of Step ST51 to Step ST54, the fixed drivepulse SP40 is output in Step ST7. Meanwhile, when the non-rotation isdetermined in Step ST35 (Step ST35: N), the correction pulse FP isoutput in Step ST6, to thereby achieve the rotational drive by 360° perstep.

In this case, when the rotation determination is made before 4.75 mshave elapsed from the start of the rotation in Step ST35, it isestimated that the drive force is in a low condition for some reason,for example, due to a low power supply voltage. Under such condition,there is a fear that a certain problem may be caused by the temporaryreduction in power supply voltage due to the large current consumption.

In view of this, after the variable drive pulse SP30 set to have alength of 5 ms is output in Step ST55, the processing proceeds to StepST71, and the fixed drive pulse SP90 based on the drive waveform for alow current, which is illustrated in FIG. 33, is output after beingswitched from the variable drive pulse SP30. In the drive based on thefixed drive pulse SP90, two coils are not simultaneously excited, andthe temporary reduction in voltage hardly occurs.

[Description of Pulse Waveforms in Eighth Embodiment: FIG. 36]

FIG. 36 is an illustration of the pulse waveforms in the eighthembodiment. In FIG. 36, waveforms (1) to (3) are illustrated as examplesof drive pulses to be applied to the stepper motor 20 when the rotationof the rotor 21 is determined. Further, a waveform (4) indicates atiming to apply the correction pulse FP, and a waveform (5) indicates atiming to apply the detection pulse CP.

In this case, as indicated by the waveforms (1) and (2), when therotation determination is made before an elapse of 3.75 ms from thestart of the rotation with the length of the variable drive pulse SP30being 4 ms or less, the fixed drive pulse SP40 is output immediatelyafter the variable drive pulse SP30 is output, and two coils aresimultaneously excited, to thereby perform the drive by 360° per step.

In contrast, as indicated by the waveform (3), when the rotationdetermination is made after an elapse of 3.75 ms from the start of therotation with the length of the variable drive pulse SP30 being as longas 5 ms, the fixed drive pulse to be output after the variable drivepulse SP30 is the fixed drive pulse SP90 based on the drive waveform fora low current, and the drive by 360° per step is performed without thesimultaneous excitation of two coils. In this case, the length of thefixed drive pulse SP40 indicated by the waveforms (1) and (2) is 3.5 ms,while the length of the fixed drive pulse SP90 indicated by the waveform(3) is as long as 7.0 ms so that the rotor 21 can be reliably rotatedeven with a low current.

With this configuration, only by detecting the timing for the rotationdetection without directly detecting the value of the power supplyvoltage and the temperature of the electronic watch, it is possible todetermine the condition in which temporary reduction in power supplyvoltage becomes a problem, to thereby avoid the problem of the temporaryreduction in power supply voltage due to the large current consumption,while it is possible to achieve a stable high-speed rotation by 360° perstep. With this, it is possible to achieve miniaturization and reductionin cost by reducing the circuit scales of, for example, a detectioncircuit for a power supply voltage and a determination circuit for atemperature.

The condition for using the fixed drive pulse SP90 based on the drivewaveform for a low current by switching the fixed drive pulse from thefixed drive pulse SP40 is not limited to the above-mentioned case inwhich the rotation determination cannot be made before an elapse of 3.75ms from the start of the rotation, and may be changed as appropriate.For example, when the rotation determination cannot be made before anelapse of 2.75 ms from the start of the rotation (Step ST34 in FIG. 35:Y), the processing may proceed to Step ST71 to use the fixed drive pulseSP90.

Modification Example of Eighth Embodiment: FIG. 36

In the eighth embodiment described above, when it is estimated that thecondition in which the temporary reduction in power supply voltagebecomes a problem has been satisfied, the fixed drive pulse SP90 basedon the drive waveform for a low current is used, but a variable drivepulse SP30′ to be applied to a reversed terminal may be output instead.

[Description of Flow of High-Speed Drive Pulse Train Output inModification Example of Eighth Embodiment: FIG. 37]

FIG. 37 is a flow chart for illustrating a flow of high-speed drivepulse train output in a modification example of the eighth embodiment.This flow is different from that of the eighth embodiment, which isillustrated in FIG. 35, only in that Step ST72 is used in place of StepST71, and the other points are the same.

That is, when the rotation determination is made before 4.75 ms haveelapsed from the start of the rotation in Step ST35 (Step ST35: Y), therotation detection is ended (Step ST45), the width of a variable drivepulse SP is set to 5 ms, the variable drive pulse SP is output, and thenthe variable drive pulse SP30′ to be applied to the switched coil isoutput.

In this case, a normal variable drive pulse is applied to any one of thecoil A and the coil B (in this case, coil B), and hence the “variabledrive pulse SP30′ to be applied to the switched coil” refers to thevariable drive pulse SP30′ to be applied to a coil that has been changedso that the variable drive pulse SP30′ is to be applied to the othercoil (in this case, coil A).

More specifically, the variable drive pulse SP30′ is obtained byreplacing the drive waveforms O1 and O2 of the variable drive pulse SP30by the drive waveforms O3 and O4, respectively, and replacing the drivewaveforms O3 and 4 of the variable drive pulse SP30 by the drivewaveforms O1 and O2, respectively. In addition, the variable drive pulseSP30′ is a drive pulse for rotating, when the rotor 21 is located at theposition of the 180°, the rotor 21 further by 180° in thecounterclockwise direction to reach the position 360° (0°).

That is, the rotor 21 has been rotated up to 135° under a state in whichthe normal variable drive pulse SP30 having a width of 5 ms is output inStep ST55, and is expected to be then rotated to reach the position of180° being the statically stable point by a holding torque. Thus, byfurther applying the variable drive pulse SP30′ from that state, it ispossible to rotate the rotor 21 up to the position of 315° and thenrotate the rotor 21 to reach the position of 360° (0°) being thestatically stable point by a holding torque.

[Description of Pulse Waveforms in Modification Example of EighthEmbodiment: FIG. 38]

FIG. 38 is a diagram for illustrating pulse waveforms in themodification example of the eighth embodiment. This flow is differentfrom that of the eighth embodiment, which is illustrated in FIG. 37,only in the waveform (3), and the other points are the same.

That is, when the rotation determination is made after an elapse of 3.75ms from the start of the rotation, which is indicated by the waveform(3), the variable drive pulse SP30 having a width of 5 ms is followed bya period of 8 ms during which the pulse is not applied, which isprovided as a period until the rotor 21 reaches a statically stableposition, and then the variable drive pulse SP30′ is output. Thevariable drive pulse SP30 and the variable drive pulse SP30′ are notused for simultaneously exciting two coils, and hence in themodification example of the eighth embodiment, in the same manner as inthe case described above in the eighth embodiment, only by detecting thetiming for the rotation detection without directly detecting the valueof the power supply voltage and the temperature of the electronic watch,it is possible to determine the condition in which temporary reductionin power supply voltage becomes a problem, to thereby avoid the problemof the temporary reduction in power supply voltage due to the largecurrent consumption, while it is possible to achieve a stable high-speedrotation by 360° per step.

The configuration diagram, the circuit diagram, the waveform diagram,and the like represented in each embodiment of the present invention arenot limited to those described above, and can be changed as appropriateas long as the gist of the present invention is satisfied.

The invention claimed is:
 1. An electronic watch, comprising: a two-coilstepper motor including: a rotor magnetized into two poles or more in aradial direction of the rotor; a stator including: a first statormagnetic-pole portion and a second stator magnetic-pole portion, whichare formed so as to oppose to each other through the rotor; and a thirdstator magnetic-pole portion, which is formed between the first statormagnetic-pole portion and the second stator magnetic-pole portion so asto face the rotor; a first coil to be magnetically coupled to the firststator magnetic-pole portion and the third stator magnetic-pole portion;and a second coil to be magnetically coupled to the second statormagnetic-pole portion and the third stator magnetic-pole portion; and adrive pulse generation circuit configured to output a drive pulse fordriving the rotor to the first coil or the second coil, wherein thedrive pulse includes a plurality of drive pulses, and wherein the rotoris to be rotationally driven in increments of 360° due to a drive pulsetrain formed of the plurality of drive pulses.
 2. The electronic watchaccording to claim 1, wherein the drive pulse train is formed of threedrive pulses of the plurality of drive pulses.
 3. The electronic watchaccording to claim 1, wherein the electronic watch is configured toswitch between high-speed drive, in which the rotor is to berotationally driven in increments of 360°, and normal drive, in whichthe rotor is to be rotationally driven in increments of 180°, andwherein the rotor is to be driven in the high-speed drive at a frequencyhigher than in the normal drive.
 4. The electronic watch according toclaim 3, further comprising: a first two-coil stepper motor to besubjected to the high-speed drive; and a second two-coil stepper motorto be subjected to the normal drive, wherein a drive frequency of thesecond two-coil stepper motor is lower than a drive frequency of thefirst two-coil stepper motor.
 5. The electronic watch according to claim1, wherein the electronic watch is configured to select a high-speeddrive pulse train or a normal drive pulse by switching a timing toselect a specific drive pulse from the drive pulse train.
 6. Theelectronic watch according to claim 1, wherein one terminal of the firstcoil and one terminal of the second coil are short-circuited.
 7. Theelectronic watch according to claim 6, wherein at least one of theplurality of drive pulses included in the drive pulse train is formed ofa pulse for exciting the first coil and a pulse for exciting the secondcoil so as to be alternately repeated.
 8. The electronic watch accordingto claim 1, further comprising: a detection pulse generation circuitconfigured to generate a detection pulse for detecting rotation of therotor; and a rotation detection determination circuit configured todetermine rotation or non-rotation of the rotor based on a detectionsignal detected by applying the detection pulse to the first coil or thesecond coil, wherein the electronic watch has a variable drive pulseformed of a part of the plurality of drive pulses included in the drivepulse train, and the variable drive pulse has a length changed dependingon a result of determining the rotation or non-rotation of the rotor bythe rotation detection determination circuit.
 9. The electronic watchaccording to claim 1, wherein the drive pulse train has a duty cycle tobe switched based on at least any one of a power supply voltage or atemperature.
 10. The electronic watch according to claim 9, wherein thedrive pulse train has the duty cycle to be further changed based on anelapsed time from a start of the rotation.
 11. The electronic watchaccording to claim 1, wherein the electronic watch has a first drivepulse train for simultaneously exciting the first coil and the secondcoil and a second drive pulse train for avoiding simultaneously excitingthe first coil and the second coil, and wherein the electronic watch isconfigured to select which one of the first drive pulse train and thesecond drive pulse train is to be used as the drive pulse train based onat least any one of a power supply voltage or a temperature.
 12. Theelectronic watch according to claim 8, wherein the variable drive pulseincludes the drive pulse train for avoiding simultaneously exciting thefirst coil and the second coil, wherein the electronic watch has, asfixed drive pulses formed of remaining drive pulses of the plurality ofdrive pulses included in the drive pulse train, a first fixed drivepulse for simultaneously exciting the first coil and the second coil anda second fixed drive pulse for avoiding simultaneously exciting thefirst coil and the second coil, and wherein the variable drive pulse isto be used irrespective of a condition, and which one of the first fixeddrive pulse and the second fixed drive pulse is to be used as the fixeddrive pulse is selected based on an elapsed time from a start of therotation.
 13. The electronic watch according to claim 8, wherein thevariable drive pulse includes the drive pulse train for avoidingsimultaneously exciting the first coil and the second coil, wherein theelectronic watch has: a fixed drive pulse formed of a remaining drivepulse of the plurality of drive pulses included in the drive pulsetrain; and a second variable drive pulse to be applied to a coildifferent from a coil to which the variable drive pulse is to beapplied, and wherein the variable drive pulse is to be used irrespectiveof a condition, and which one of the fixed drive pulse and the secondvariable drive pulse is to be used is selected based on an elapsed timefrom a start of the rotation.